Method and apparatus for controlling uplink transmission power in wireless access system supporting machine-type communication

ABSTRACT

A method performed by a user equipment (UE) is provided. The UE controls uplink transmission power by receiving control information for a Physical Uplink Shared Channel (PUSCH), and repeatedly transmitting a PUSCH as a predetermined number of times based on the control information. The PUSCH is repeatedly transmitted with a transmission power which is maintained constant during a time period for the repeated PUSCH transmissions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is Continuation of U.S. application Ser. No.15/101,834, filed on Jun. 3, 2016, which is the National Phase of PCTInternational Application No. PCT/KR2014/011906, filed on Dec. 5, 2014,which claims priority under 35 U.S.C. 119(e) to U.S. ProvisionalApplication No. 61/912,536, filed on Dec. 5, 2013 and 61/914,379 filedon Dec. 10, 2013, all of which are hereby expressly incorporated byreference into the present application.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates generally to a wireless access systemsupporting Machine Type Communication (MTC), and more particularly, tomethods for controlling uplink transmission power by an MTC terminal,and apparatuses supporting the methods.

Background Art

Wireless access systems have been widely deployed to provide varioustypes of communication services such as voice or data. In general, awireless access system is a multiple access system that supportscommunication of multiple users by sharing available system resources (abandwidth, transmission power, etc.) among them. For example, multipleaccess systems include a Code Division Multiple Access (CDMA) system, aFrequency Division Multiple Access (FDMA) system, a Time DivisionMultiple Access (TDMA) system, an Orthogonal Frequency Division MultipleAccess (OFDMA) system, and a Single Carrier Frequency Division MultipleAccess (SC-FDMA) system.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method forefficiently transmitting and receiving data in a wireless access systemsupporting Machine Type Communication (MTC).

Another object of the present invention is to provide a method forcontrolling uplink transmission power of an MTC terminal.

Another object of the present invention is to provide apparatusessupporting the above methods.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present invention are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present invention could achieve will be more clearlyunderstood from the following detailed description.

The present invention relates to a wireless access system supportingMachine Type Communication (MTC). More particularly, the presentinvention provides methods for controlling uplink transmission power byan MTC terminal, and apparatuses supporting the methods.

In an aspect of the present invention, provided herein is a method forcontrolling uplink transmission power by a Machine Type Communication(MTC) User Equipment (UE) in a wireless access system supporting MTC,including receiving a first downlink control channel including a firstTransmit Power Command (TPC), repeatedly a predetermined number oftimes, transmitting a first uplink channel according to transmissionpower indicated by the first TPC, repeatedly a predetermined number oftimes, and receiving a second downlink control channel including asecond TPC indicating adjustment of the transmission power during thepredetermined number of repeated transmissions of the first uplinkchannel. The first uplink channel is transmitted according to thetransmission power indicated by the first TPC, without reflecting thesecond TPC during the repeated transmissions of the first uplinkchannel.

The method may further include, after completion of the repeatedtransmissions of the first uplink channel, receiving a third downlinkcontrol channel including a third TPC indicating adjustment of thetransmission power.

The method may further include transmitting a second uplink channelrepeatedly a predetermined number of times, in consideration of both ofa transmission power control value indicated by the second TPC and atransmission power control value indicated by the third TPC.

Or the method may further include transmitting a second uplink channelrepeatedly a predetermined number of times according to transmissionpower adjusted according to a transmission power control value indicatedby the third TPC.

In another aspect of the present invention, an MTC UE for controllinguplink transmission power in a wireless access system supporting MTCincludes a receiver, a transmitter, and a processor configured tocontrol uplink transmission power.

The processor may be configured to receive a first downlink controlchannel including a first TPC, repeatedly a predetermined number oftimes by controlling the receiver, to transmit a first uplink channelaccording to transmission power indicated by the first TPC, repeatedly apredetermined number of times by controlling the transmitter, and uponreceipt of a second downlink control channel including a second TPCindicating adjustment of the transmission power during the predeterminednumber of repeated transmissions of the first uplink channel, totransmit the first uplink channel according to the transmission powerindicated by the first TPC by controlling the transmitter, withoutreflecting the second TPC during the repeated transmissions of the firstuplink channel.

After completion of the repeated transmissions of the first uplinkchannel, the processor may be configured to control the receiver toreceive a third downlink control channel including a third TPCindicating adjustment of the transmission power.

Also, the processor may be configured to control the transmitter totransmit a second uplink channel repeatedly a predetermined number oftimes, in consideration of both of a transmission power control valueindicated by the second TPC and a transmission power control valueindicated by the third TPC.

Or the processor may be configured to control the transmitter totransmit a second uplink channel repeatedly a predetermined number oftimes according to transmission power adjusted according to atransmission power control value indicated by the third TPC.

According to the above aspects of the present invention, the downlinkcontrol channel may be a Physical Downlink Control Channel (PDCCH)transmitted in a control channel region of a subframe, or an EnhancedPDCCH (E-PDCCH) transmitted in a data channel region of a subframe, andthe uplink channel may be a Physical Uplink Control Channel (PUCCH) fortransmitting uplink control information or a Physical Uplink SharedChannel (PUSCH) for transmitting user data.

If the first uplink channel is the PUSCH and the repeated transmissionsof the first uplink channel overlap with the repeated transmissions ofthe PUCCH, the repeated transmissions of the first uplink channel may bediscontinued and the repeated transmissions of the PUCCH may beperformed.

Also, the first uplink channel may be transmitted with transmissionpower increased by as much as the number of overlapped subframes.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

As is apparent from the above description, the embodiments of thepresent invention have the following effects.

First, a Machine Type Communication (MTC) terminal can perform uplinktransmission reliably and efficiently.

Secondly, even though an MTC terminal receives a Transmit Power Command(TPC) indicating transmission power adjustment during repeatedtransmissions of an uplink channel, the MTC terminal can continuetransmission of the uplink channel, ignoring the TPC command.

Thirdly, if uplink channels are overlapped with each other, an MTCterminal transmits an uplink channel, taking into account the prioritylevels of the uplink channels, and increases the transmission power of atransmission-discontinued uplink channel in proportion to the number ofoverlapped subframes. Therefore, the discontinued transmission of theuplink channel can be compensated.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the technical features or scope of theinventions. Thus, it is intended that the present invention covers themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 is a conceptual diagram illustrating physical channels used inthe embodiments and a signal transmission method using the physicalchannels.

FIG. 2 is a diagram illustrating a structure of a radio frame for use inthe embodiments.

FIG. 3 is a diagram illustrating an example of a resource grid of adownlink slot according to the embodiments.

FIG. 4 is a diagram illustrating a structure of an uplink subframeaccording to the embodiments.

FIG. 5 is a diagram illustrating a structure of a downlink subframeaccording to the embodiments.

FIG. 6 illustrates PUCCH formats 1a and 1b for use in a normal CyclicPrefix (CP) case, and FIG. 7 illustrates Physical Uplink Control Channel(PUCCH) formats 1a and 1b for use in an extended CP case.

FIG. 8 illustrates PUCCH formats 2/2a/2b in a normal CP case, and FIG. 9illustrates PUCCH formats 2/2a/2b in an extended CP case.

FIG. 10 illustrates Acknowledgment/Negative Acknowledgment (ACK/NACK)channelization for PUCCH formats 1a and 1b.

FIG. 11 illustrates channelization for a hybrid structure of PUCCHformat 1a/1b and format 2/2a/2b in the same Physical Resource Block(PRB).

FIG. 12 illustrates allocation of a PRB.

FIG. 13 is a diagram illustrating an example of a Component Carrier (CC)of the embodiments and Carrier Aggregation (CA) used in a Long TermEvolution-Advanced (LTE-A) system.

FIG. 14 illustrates a subframe structure of an LTE-A system according tocross-carrier scheduling.

FIG. 15 is conceptual diagram illustrating a construction of servingcells according to cross-carrier scheduling.

FIG. 16 is a conceptual diagram illustrating CA PUCCH signal processing.

FIG. 17 is a diagram illustrating a signal flow for a method ofadjusting uplink transmission power.

FIG. 18 is a diagram illustrating one of methods of adjusting thetransmission power of a PUSCH, when repeated PUCCH transmissions collidewith repeated PUSCH transmissions.

FIG. 19 is a diagram illustrating one of methods of adjusting thetransmission power of a PUSCH, when repeated PUCCH transmissions collidewith repeated PUSCH transmissions.

FIG. 20 is a block diagram of apparatuses for implementing the methodsillustrated in FIGS. 1 to 19.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention described below in detail relate toa wireless access system supporting Machine Type Communication (MTC).More particularly, the embodiments of the present invention relate tomethods of controlling uplink transmission power by an MTC terminal, andapparatuses supporting the methods.

The embodiments of the present disclosure described below arecombinations of elements and features of the present disclosure inspecific forms. The elements or features may be considered selectiveunless otherwise mentioned. Each element or feature may be practicedwithout being combined with other elements or features. Further, anembodiment of the present disclosure may be constructed by combiningparts of the elements and/or features. Operation orders described inembodiments of the present disclosure may be rearranged. Someconstructions or elements of any one embodiment may be included inanother embodiment and may be replaced with corresponding constructionsor features of another embodiment.

In the description of the attached drawings, a detailed description ofknown procedures or steps of the present disclosure will be avoided lestit should obscure the subject matter of the present disclosure. Inaddition, procedures or steps that could be understood to those skilledin the art will not be described either.

Throughout the specification, when a certain portion “includes” or“comprises” a certain component, this indicates that other componentsare not excluded and may be further included unless otherwise noted. Theterms “unit”, “-or/er” and “module” described in the specificationindicate a unit for processing at least one function or operation, whichmay be implemented by hardware, software or a combination thereof. Inaddition, the terms “a or an”, “one”, “the” etc. may include a singularrepresentation and a plural representation in the context of the presentinvention (more particularly, in the context of the following claims)unless indicated otherwise in the specification or unless contextclearly indicates otherwise.

In the embodiments of the present disclosure, a description is mainlymade of a data transmission and reception relationship between a BaseStation (BS) and a User Equipment (UE). A BS refers to a terminal nodeof a network, which directly communicates with a UE. A specificoperation described as being performed by the BS may be performed by anupper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS, or network nodesother than the BS. The term ‘BS’ may be replaced with a fixed station, aNode B, an evolved Node B (eNode B or eNB), an Advanced Base Station(ABS), an access point, etc.

In the embodiments of the present disclosure, the term terminal may bereplaced with a UE, a Mobile Station (MS), a Subscriber Station (SS), aMobile Subscriber Station (MSS), a mobile terminal, an Advanced MobileStation (AMS), etc.

A transmitter is a fixed and/or mobile node that provides a data serviceor a voice service and a receiver is a fixed and/or mobile node thatreceives a data service or a voice service. Therefore, a UE may serve asa transmitter and a BS may serve as a receiver, on an UpLink (UL).Likewise, the UE may serve as a receiver and the BS may serve as atransmitter, on a DownLink (DL).

The embodiments of the present disclosure may be supported by standardspecifications disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802.xx system, a 3^(rd) Generation Partnership Project (3GPP) system, a3GPP Long Term Evolution (LTE) system, and a 3GPP2 system. Inparticular, the embodiments of the present disclosure may be supportedby the standard specifications, 3GPP TS 36.211, 3GPP TS 36.212, 3GPP TS36.213, 3GPP TS 36.321 and 3GPP TS 36.331. That is, the steps or parts,which are not described to clearly reveal the technical idea of thepresent disclosure, in the embodiments of the present disclosure may beexplained by the above standard specifications. All terms used in theembodiments of the present disclosure may be explained by the standardspecifications.

Reference will now be made in detail to the embodiments of the presentdisclosure with reference to the accompanying drawings. The detaileddescription, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present disclosure, rather than to show the only embodiments thatcan be implemented according to the invention.

The following detailed description includes specific terms in order toprovide a thorough understanding of the present disclosure. However, itwill be apparent to those skilled in the art that the specific terms maybe replaced with other terms without departing the technical spirit andscope of the present disclosure.

For example, a general UE refers to a device supporting communicationservice for a user in an LTE/LTE-A system, whereas an MTC UE refers to adevice that operates in the LTE/LTE-A system and is equipped only withmandatory functions for supporting MTC, and a function for coverageextension. Further, the terms, multiplex and piggyback areinterchangeably used with each other in similar meanings.

Hereinafter, 3GPP LTE/LTE-A systems which are examples of a wirelessaccess system which can be applied to embodiments to the presentinvention will be explained.

The embodiments of the present disclosure can be applied to variouswireless access systems such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), etc.

CDMA may be implemented as a radio technology such as UniversalTerrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented asa radio technology such as Global System for Mobile communications(GSM)/General packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be implemented as a radio technology such asIEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Evolved UTRA(E-UTRA), etc.

UTRA is a part of Universal Mobile Telecommunications System (UMTS).3GPP LTE is a part of Evolved UMTS (E-UMTS) using E-UTRA, adopting OFDMAfor DL and SC-FDMA for UL. LTE-Advanced (LTE-A) is an evolution of 3GPPLTE. While the embodiments of the present disclosure are described inthe context of a 3GPP LTE/LTE-A system in order to clarify the technicalfeatures of the present disclosure, the present disclosure is alsoapplicable to an IEEE 802.16e/m system, etc.

1. 3GPP LTE/LTE-A System

In a wireless access system, a UE receives information from an eNB on aDL and transmits information to the eNB on a UL. The informationtransmitted and received between the UE and the eNB includes generaldata information and various types of control information. There aremany physical channels according to the types/usages of informationtransmitted and received between the eNB and the UE.

1.1 System Overview

FIG. 1 illustrates physical channels and a general method using thephysical channels, which may be used in embodiments of the presentdisclosure.

When a UE is powered on or enters a new cell, the UE performs initialcell search (S11). The initial cell search involves acquisition ofsynchronization to an eNB. Specifically, the UE synchronizes its timingto the eNB and acquires information such as a cell Identifier (ID) byreceiving a Primary Synchronization Channel (P-SCH) and a SecondarySynchronization Channel (S-SCH) from the eNB.

Then the UE may acquire information broadcast in the cell by receiving aPhysical Broadcast Channel (PBCH) from the eNB.

During the initial cell search, the UE may monitor a DL channel state byreceiving a Downlink Reference Signal (DL RS).

After the initial cell search, the UE may acquire more detailed systeminformation by receiving a Physical Downlink Control Channel (PDCCH) andreceiving a Physical Downlink Shared Channel (PDSCH) based oninformation of the PDCCH (S12).

To complete connection to the eNB, the UE may perform a random accessprocedure with the eNB (S13 to S16). In the random access procedure, theUE may transmit a preamble on a Physical Random Access Channel (PRACH)(S13) and may receive a PDCCH and a PDSCH associated with the PDCCH(S14). In the case of contention-based random access, the UE mayadditionally perform a contention resolution procedure includingtransmission of an additional PRACH (S15) and reception of a PDCCHsignal and a PDSCH signal corresponding to the PDCCH signal (S16).

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the eNB (S17) and transmit a Physical Uplink Shared Channel (PUSCH)and/or a Physical Uplink Control Channel (PUCCH) to the eNB (S18), in ageneral UL/DL signal transmission procedure.

Control information that the UE transmits to the eNB is genericallycalled Uplink Control Information (UCI). The UCI includes a HybridAutomatic Repeat and reQuest Acknowledgement/Negative Acknowledgement(HARQ-ACK/NACK), a Scheduling Request (SR), a Channel Quality Indicator(CQI), a Precoding Matrix Index (PMI), a Rank Indicator (RI), etc.

In the LTE system, UCI is generally transmitted on a PUCCH periodically.However, if control information and traffic data should be transmittedsimultaneously, the control information and traffic data may betransmitted on a PUSCH. In addition, the UCI may be transmittedaperiodically on the PUSCH, upon receipt of a request/command from anetwork.

FIG. 2, including views (a) and (b), illustrates exemplary radio framestructures used in embodiments of the present disclosure.

FIG. 2(a) illustrates frame structure type 1. Frame structure type 1 isapplicable to both a full Frequency Division Duplex (FDD) system and ahalf FDD system.

One radio frame is 10 ms (T_(f)=307200·T_(s)) long, includingequal-sized 20 slots indexed from 0 to 19. Each slot is 0.5 ms(T_(slot)=15360·T_(s)) long. One subframe includes two successive slots.An i^(th) subframe includes 2i^(th) and (2i+1)^(th) slots. That is, aradio frame includes 10 subframes. A time required for transmitting onesubframe is defined as a Transmission Time Interval (TTI). T_(s) is asampling time given as T_(s)=1/(15 kHz×2048)=3.2552×10⁻⁸ (about 33 ns).One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols or SC-FDMA symbols in the time domain by aplurality of Resource Blocks (RBs) in the frequency domain.

A slot includes a plurality of OFDM symbols in the time domain. SinceOFDMA is adopted for DL in the 3GPP LTE system, one OFDM symbolrepresents one symbol period. An OFDM symbol may be called an SC-FDMAsymbol or symbol period. An RB is a resource allocation unit including aplurality of contiguous subcarriers in one slot.

In a full FDD system, each of 10 subframes may be used simultaneouslyfor DL transmission and UL transmission during a 10-ms duration. The DLtransmission and the UL transmission are distinguished by frequency. Onthe other hand, a UE cannot perform transmission and receptionsimultaneously in a half FDD system.

The above radio frame structure is purely exemplary. Thus, the number ofsubframes in a radio frame, the number of slots in a subframe, and thenumber of OFDM symbols in a slot may be changed.

FIG. 2(b) illustrates frame structure type 2. Frame structure type 2 isapplied to a Time Division Duplex (TDD) system. One radio frame is 10 ms(T_(f)=307200·T_(s)) long, including two half-frames each having alength of 5 ms (=153600·T_(s)) long. Each half-frame includes fivesubframes each being 1 ms (=30720·T_(s)) long. An i^(th) subframeincludes 2i^(th) and (2i+1)^(th) slots each having a length of 0.5 ms(T_(slot)=15360·T_(s)). T_(s) is a sampling time given as T_(s)=1/(15kHz×2048)=3.2552×10⁻⁸ (about 33 ns).

A type-2 frame includes a special subframe having three fields, DownlinkPilot Time Slot (DwPTS), Guard Period (GP), and Uplink Pilot Time Slot(UpPTS). The DwPTS is used for initial cell search, synchronization, orchannel estimation at a UE, and the UpPTS is used for channel estimationand UL transmission synchronization with a UE at an eNB. The GP is usedto cancel UL interference between a UL and a DL, caused by themulti-path delay of a DL signal.

[Table 1] below lists special subframe configurations (DwPTS/GP/UpPTSlengths).

TABLE 1 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Special Normal Extended Normal Extended subframecyclic prefix cyclic prefix cyclic prefix cyclic prefix configurationDwPTS in uplink in uplink DwPTS in uplink in uplink 0  6592 · T_(s) 2192· T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 · T_(s) 5  6592· T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

FIG. 3 illustrates an exemplary structure of a DL resource grid for theduration of one DL slot, which may be used in embodiments of the presentdisclosure.

Referring to FIG. 3, a DL slot includes a plurality of OFDM symbols inthe time domain. One DL slot includes 7 OFDM symbols in the time domainand an RB includes 12 subcarriers in the frequency domain, to which thepresent disclosure is not limited.

Each element of the resource grid is referred to as a Resource Element(RE). An RB includes 12×7 REs. The number of RBs in a DL slot, N_(DL)depends on a DL transmission bandwidth. A UL slot may have the samestructure as a DL slot.

FIG. 4 illustrates a structure of a UL subframe which may be used inembodiments of the present disclosure.

Referring to FIG. 4, a UL subframe may be divided into a control regionand a data region in the frequency domain. A PUCCH carrying UCI isallocated to the control region and a PUSCH carrying user data isallocated to the data region. To maintain a single carrier property, aUE does not transmit a PUCCH and a PUSCH simultaneously. A pair of RBsin a subframe are allocated to a PUCCH for a UE. The RBs of the RB pairoccupy different subcarriers in two slots. Thus it is said that the RBpair frequency-hops over a slot boundary.

FIG. 5 illustrates a structure of a DL subframe that may be used inembodiments of the present disclosure.

l Referring to FIG. 5, up to three OFDM symbols of a DL subframe,starting from OFDM symbol 0 are used as a control region to whichcontrol channels are allocated and the other OFDM symbols of the DLsubframe are used as a data region to which a PDSCH is allocated. DLcontrol channels defined for the 3GPP LTE system include a PhysicalControl Format Indicator Channel (PCFICH), a PDCCH, and a PhysicalHybrid ARQ Indicator Channel (PHICH).

The PCFICH is transmitted in the first OFDM symbol of a subframe,carrying information about the number of OFDM symbols used fortransmission of control channels (i.e. the size of the control region)in the subframe. The PHICH is a response channel to a UL transmission,delivering an HARQ ACK/NACK signal. Control information carried on thePDCCH is called Downlink Control Information (DCI). The DCI transportsUL resource assignment information, DL resource assignment information,or UL Transmission (Tx) power control commands for a UE group.

1.2 Physical Downlink Control Channel (PDCCH)

1.2.1 PDCCH Overview

The PDCCH may deliver information about resource allocation and atransport format for a Downlink Shared Channel (DL-SCH) (i.e. a DLgrant), information about resource allocation and a transport format foran Uplink Shared Channel (UL-SCH) (i.e. a UL grant), paging informationof a Paging Channel (PCH), system information on the DL-SCH, informationabout resource allocation for a higher layer control message such as arandom access response transmitted on the PDSCH, a set of Tx powercontrol commands for individual UEs of a UE group, Voice Over InternetProtocol (VoIP) activation indication information, etc.

A plurality of PDCCHs may be transmitted in the control region. A UE maymonitor a plurality of PDCCHs. A PDCCH is transmitted in an aggregate ofone or more consecutive Control Channel Elements (CCEs). A PDCCH made upof one or more consecutive CCEs may be transmitted in the control regionafter subblock interleaving. A CCE is a logical allocation unit used toprovide a PDCCH at a code rate based on the state of a radio channel. ACCE includes a plurality of RE Groups (REGs). The format of a PDCCH andthe number of available bits for the PDCCH are determined according tothe relationship between the number of CCEs and a code rate provided bythe CCEs.

1.2.2 PDCCH Structure

A plurality of PDCCHs for a plurality of UEs may be multiplexed andtransmitted in the control region. A PDCCH is made up of an aggregate ofone or more consecutive CCEs. A CCE is a unit of 9 REGs each REGincluding 4 REs. Four Quadrature Phase Shift Keying (QPSK) symbols aremapped to each REG. REs occupied by RSs are excluded from REGs. That is,the total number of REGs in an OFDM symbol may be changed depending onthe presence or absence of a cell-specific RS. The concept of an REG towhich four REs are mapped is also applicable to other DL controlchannels (e.g. the PCFICH or the PHICH). Let the number of REGs that arenot allocated to the PCFICH or the PHICH be denoted by N_(REG). Then thenumber of CCEs available to the system is N_(CCE) (=└_(REG)/9 ┘) and theCCEs are indexed from 0 to N_(CCE)−1.

To simplify the decoding process of a UE, a PDCCH format including nCCEs may start with a CCE having an index equal to a multiple of n. Thatis, given CCE i, the PDCCH format may start with a CCE satisfying i modn=0.

The eNB may configure a PDCCH with 1, 2, 4, or 8 CCEs. {1, 2, 4, 8} arecalled CCE aggregation levels. The number of CCEs used for transmissionof a PDCCH is determined according to a channel state by the eNB. Forexample, one CCE is sufficient for a PDCCH directed to a UE in a good DLchannel state (a UE near to the eNB). On the other hand, 8 CCEs may berequired for a PDCCH directed to a UE in a poor DL channel state (a UEat a cell edge) in order to ensure sufficient robustness.

[Table 2] below illustrates PDCCH formats. 4 PDCCH formats are supportedaccording to CCE aggregation levels as illustrated in [Table 2].

TABLE 2 Number of PDCCH format Number of CCEs (n) Number of REGs PDCCHbits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

A different CCE aggregation level is allocated to each UE because theformat or Modulation and Coding Scheme (MCS) level of controlinformation delivered in a PDCCH for the UE is different. An MCS leveldefines a code rate used for data coding and a modulation order. Anadaptive MCS level is used for link adaptation. In general, three orfour MCS levels may be considered for control channels carrying controlinformation.

Regarding the formats of control information, control informationtransmitted on a PDCCH is called DCI. The configuration of informationin PDCCH payload may be changed depending on the DCI format. The PDCCHpayload is information bits. [Table 3] lists DCI according to DCIformats.

TABLE 3 DCI Format Description Format 0 Resource grants for the PUSCHtransmissions (uplink) Format 1 Resource assignments for single codewordPDSCH transmissions (transmission modes 1, 2 and 7) Format Compactsignaling of resource assignments for single 1A codeword PDSCH (allmodes) Format Compact resource assignments for PDSCH using rank-1 1Bclosed loop precoding (mode 6) Format Very compact resource assignmentsfor PDSCH (e.g. 1C paging/broadcast system information) Format Compactresource assignments for PDSCH using multi-user 1D MIMO (mode 5) Format2 Resource assignments for PDSCH for closed-loop MIMO operation (mode 4)Format Resource assignments for PDSCH for open-loop MIMO 2A operation(mode 3) Format Power control commands for PUCCH and PUSCH with 3/3A2-bit/1-bit power adjustment Format 4 Scheduling of PUSCH in one UL cellwith multi-antenna port transmission mode

Referring to [Table 3], the DCI formats include Format 0 for PUSCHscheduling, Format 1 for single-codeword PDSCH scheduling, Format 1A forcompact single-codeword PDSCH scheduling, Format 1C for very compactDL-SCH scheduling, Format 2 for PDSCH scheduling in a closed-loopspatial multiplexing mode, Format 2A for PDSCH scheduling in anopen-loop spatial multiplexing mode, and Format 3/3A for transmission ofTransmission Power Control (TPC) commands for uplink channels. DCIFormat 1A is available for PDSCH scheduling irrespective of thetransmission mode of a UE.

The length of PDCCH payload may vary with DCI formats. In addition, thetype and length of PDCCH payload may be changed depending on compact ornon-compact scheduling or the transmission mode of a UE.

The transmission mode of a UE may be configured for DL data reception ona PDSCH at the UE. For example, DL data carried on a PDSCH includesscheduled data, a paging message, a random access response, broadcastinformation on a BCCH, etc. for a UE. The DL data of the PDSCH isrelated to a DCI format signaled through a PDCCH. The transmission modemay be configured semi-statically for the UE by higher layer signaling(e.g. Radio Resource Control (RRC) signaling). The transmission mode maybe classified as single antenna transmission or multi-antennatransmission.

A transmission mode is configured for a UE semi-statically by higherlayer signaling. For example, multi-antenna transmission scheme mayinclude transmit diversity, open-loop or closed-loop spatialmultiplexing, Multi-User Multiple Input Multiple Output (MU-MIMO), orbeamforming. Transmit diversity increases transmission reliability bytransmitting the same data through multiple Tx antennas. Spatialmultiplexing enables high-speed data transmission without increasing asystem bandwidth by simultaneously transmitting different data throughmultiple Tx antennas. Beamforming is a technique of increasing theSignal to Interference plus Noise Ratio (SINR) of a signal by weightingmultiple antennas according to channel states.

A DCI format for a UE depends on the transmission mode of the UE. The UEhas a reference DCI format monitored according to the transmission modeconfigure for the UE. The following 10 transmission modes are availableto UEs:

(1) Transmission mode 1: Single antenna port (port 0);

(2) Transmission mode 2: Transmit diversity;

(3) Transmission mode 3: Open-loop spatial multiplexing when the numberof layer is larger than 1 or Transmit diversity when the rank is 1;

(4) Transmission mode 4: Closed-loop spatial multiplexing;

(5) Transmission mode 5: MU-MIMO;

(6) Transmission mode 6: Closed-loop rank-1 precoding;

(7) Transmission mode 7: Precoding supporting a single layertransmission, which does not based on a codebook (Rel-8);

(8) Transmission mode 8: Precoding supporting up to two layers, which donot based on a codebook (Rel-9);

(9) Transmission mode 9: Precoding supporting up to eight layers, whichdo not based on a codebook (Rel-10); and

(10) Transmission mode 10: Precoding supporting up to eight layers,which do not based on a codebook, used for CoMP (Rel-11).

1.2.3 PDCCH Transmission

The eNB determines a PDCCH format according to DCI that will betransmitted to the UE and adds a Cyclic Redundancy Check (CRC) to thecontrol information. The CRC is masked by a unique Identifier (ID) (e.g.a Radio Network Temporary Identifier (RNTI)) according to the owner orusage of the PDCCH. If the PDCCH is destined for a specific UE, the CRCmay be masked by a unique ID (e.g. a cell-RNTI (C-RNTI)) of the UE. Ifthe PDCCH carries a paging message, the CRC of the PDCCH may be maskedby a paging indicator ID (e.g. a Paging-RNTI (P-RNTI)). If the PDCCHcarries system information, particularly, a System Information Block(SIB), its CRC may be masked by a system information ID (e.g. a SystemInformation RNTI (SI-RNTI)). To indicate that the PDCCH carries a randomaccess response to a random access preamble transmitted by a UE, its CRCmay be masked by a Random Access-RNTI (RA-RNTI).

Then the eNB generates coded data by channel-encoding the CRC-addedcontrol information. The channel coding may be performed at a code ratecorresponding to an MCS level. The eNB rate-matches the coded dataaccording to a CCE aggregation level allocated to a PDCCH format andgenerates modulation symbols by modulating the coded data. Herein, amodulation order corresponding to the MCS level may be used for themodulation. The CCE aggregation level for the modulation symbols of aPDCCH may be one of 1, 2, 4, and 8. Subsequently, the eNB maps themodulation symbols to physical REs (i.e. CCE to RE mapping).

1.2.4 Blind Decoding (BD)

A plurality of PDCCHs may be transmitted in a subframe. That is, thecontrol region of a subframe includes a plurality of CCEs, CCE 0 to CCEN_(CCE,k)−1. N_(CCE,k) is the total number of CCEs in the control regionof a k^(th) subframe. A UE monitors a plurality of PDCCHs in everysubframe. This means that the UE attempts to decode each PDCCH accordingto a monitored PDCCH format.

The eNB does not provide the UE with information about the position of aPDCCH directed to the UE in an allocated control region of a subframe.Without knowledge of the position, CCE aggregation level, or DCI formatof its PDCCH, the UE searches for its PDCCH by monitoring a set of PDCCHcandidates in the subframe in order to receive a control channel fromthe eNB. This is called blind decoding. Blind decoding is the process ofdemasking a CRC part with a UE ID, checking a CRC error, and determiningwhether a corresponding PDCCH is a control channel directed to a UE bythe UE.

The UE monitors a PDCCH in every subframe to receive data transmitted tothe UE in an active mode. In a Discontinuous Reception (DRX) mode, theUE wakes up in a monitoring interval of every DRX cycle and monitors aPDCCH in a subframe corresponding to the monitoring interval. ThePDCCH-monitored subframe is called a non-DRX subframe.

To receive its PDCCH, the UE should blind-decode all CCEs of the controlregion of the non-DRX subframe. Without knowledge of a transmitted PDCCHformat, the UE should decode all PDCCHs with all possible CCEaggregation levels until the UE succeeds in blind-decoding a PDCCH inevery non-DRX subframe. Since the UE does not know the number of CCEsused for its PDCCH, the UE should attempt detection with all possibleCCE aggregation levels until the UE succeeds in blind decoding of aPDCCH.

In the LTE system, the concept of Search Space (SS) is defined for blinddecoding of a UE. An SS is a set of PDCCH candidates that a UE willmonitor. The SS may have a different size for each PDCCH format. Thereare two types of SSs, Common Search Space (CSS) andUE-specific/Dedicated Search Space (USS).

While all UEs may know the size of a CSS, a USS may be configured foreach individual UE. Accordingly, a UE should monitor both a CSS and aUSS to decode a PDCCH. As a consequence, the UE performs up to 44 blinddecodings in one subframe, except for blind decodings based on differentCRC values (e.g., C-RNTI, P-RNTI, SI-RNTI, and RA-RNTI).

In view of the constraints of an SS, the eNB may not secure CCEresources to transmit PDCCHs to all intended UEs in a given subframe.This situation occurs because the remaining resources except forallocated CCEs may not be included in an SS for a specific UE. Tominimize this obstacle that may continue in the next subframe, aUE-specific hopping sequence may apply to the starting point of a USS.

[Table 4] illustrates the sizes of CSSs and USSs.

TABLE 4 Number PDCCH of CCEs Number of candidates Number of candidatesformat (n) in common search space in dedicated search space 0 1 — 6 1 2— 6 2 4 4 2 3 8 2 2

To mitigate the load of the UE caused by the number of blind decodingattempts, the UE does not search for all defined DCI formatssimultaneously. Specifically, the UE always searches for DCI Format 0and DCI Format 1A in a USS. Although DCI Format 0 and DCI Format 1A areof the same size, the UE may distinguish the DCI formats by a flag forformat0/format 1a differentiation included in a PDCCH. Other DCI formatsthan DCI Format 0 and DCI Format 1A, such as DCI Format 1, DCI Format1B, and DCI Format 2 may be required for the UE.

The UE may search for DCI Format 1A and DCI Format 1C in a CSS. The UEmay also be configured to search for DCI Format 3 or 3A in the CSS.Although DCI Format 3 and DCI Format 3A have the same size as DCI Format0 and DCI Format 1A, the UE may distinguish the DCI formats by a CRCscrambled with an ID other than a UE-specific ID.

An SS S_(k) ^((L)) is a PDCCH candidate set with a CCE aggregrationlevel L∈{1,2,4,9}. The CCEs of PDCCH candidate set m in the SS may bedetermined by the following equation.

L·{(Y _(k) +m)mod└N _(CCE,k) /L┘}+i   [Equation 1]

where M^((L)) is the number of PDCCH candidates with CCE aggregationlevel L to be monitored in the SS, m=0,Λ,M^((L))−1, i is the index of aCCE in each PDCCH candidate, and i=0,Λ,L−1 k=└n_(s)/2┘ where n_(s) isthe index of a slot in a radio frame.

As described before, the UE monitors both the USS and the CSS to decodea PDCCH. The CSS supports PDCCHs with CCE aggregation levels {4, 8} andthe USS supports PDCCHs with CCE aggregation levels {1, 2, 4, 8}. [Table5] illustrates PDCCH candidates monitored by a UE.

TABLE 5 Search space S_(k) ^((L)) Number of PDCCH Type Aggregation levelL Size [in CCEs] candidates M^((L)) UE- 1 6 6 specific 2 12 6 4 8 2 8 162 Common 4 16 4 8 16 2

Referring to [Equation 1], for two aggregation levels, L=4 and L=8,Y_(k) is set to 0 in the CSS, whereas Y_(k) is defined by [Equation 2]for aggregation level L in the USS.

Y _(k)=(A·Y _(k-1)) mod D   [Equation 2]

where Y₋₁=n_(RNTI)≠0, n_(RNTI) indicating an RNTI valve. A=39827 andD=65537.

1.3. PUCCH (Physical Uplink Control Channel)

PUCCH may include the following formats to transmit control information.

(1) Format 1: On-Off keying (OOK) modulation, used for SR (SchedulingRequest)

(2) Format 1a & 1b: Used for ACK/NACK transmission

-   -   1) Format 1a: BPSK ACK/NACK for 1 codeword    -   2) Format 1b: QPSK ACK/NACK for 2 codewords

(3) Format 2: QPSK modulation, used for CQI transmission

(4) Format 2a & Format 2b: Used for simultaneous transmission of CQI andACK/NACK

(5) Format 3: Used for multiple ACK/NACK transmission in a carrieraggregation environment

[Table 6] shows a modulation scheme according to PUCCH format and thenumber of bits per subframe. [Table 7] shows the number of referencesignals (RS) per slot according to PUCCH format. [Table 8] shows SC-FDMAsymbol location of RS (reference signal) according to PUCCH format. In[Table 6], PUCCH format 2a and PUCCH format 2b correspond to a case ofnormal Cyclic Prefix (CP).

TABLE 6 Modulation No. of bits per subframe, PUCCH format scheme Mbit 1N/A N/A 1a BPSK 1 1b QPSK 2 2 QPSK 20 2a QPSK + BPSK 21 2b QPSK + BPSK22 3 QPSK 48

TABLE 7 PUCCH format Normal CP Extended CP 1, 1a, 1b 3 2 2, 3 2 1 2a, 2b2 N/A

TABLE 8 SC-FDMA symbol location of RS PUCCH format Normal CP Extended CP1, 1a, 1b 2, 3, 4 2, 3 2, 3 1, 5 3 2a, 2b 1, 5 N/A

FIG. 6 shows PUCCH formats 1a and 1b in case of a normal cyclic prefix.And, FIG. 7 shows PUCCH formats 1a and 1b in case of an extended cyclicprefix.

According to the PUCCH formats 1a and 1b, control information of thesame content is repeated in a subframe by slot unit. In each UE,ACK/NACK signal is transmitted on a different resource constructed witha different Cyclic Shift (CS) (frequency domain code) and an OrthogonalCover (OC) or Orthogonal Cover Code (OCC) (time domain spreading code)of CG-CAZAC (computer-generated constant amplitude zero autocorrelation) sequence. For instance, the OC includes Walsh/DFTorthogonal code. If the number of CS and the number of OC are 6 and 3,respectively, total 18 UEs may be multiplexed within the same PRB(physical resource block) with reference to a single antenna. Orthogonalsequences w0, w1, w2 and w3 may be applicable to a random time domain(after FFT modulation) or a random frequency domain (before FFTmodulation).

For persistent scheduling with SR, ACK/NACK resource constructed withCS, OC and Physical resource Block (PRB) may be allocated to a UEthrough Radio Resource Control (RRC). For non-persistent scheduling withdynamic ACK/NACK, the ACK/NACK resource may be implicitly allocated to aUE using a smallest CCE index of PDCCH corresponding to PDSCH.

Length-4 orthogonal sequence (OC) and length-3 orthogonal sequence forPUCCH format 1/1a/1b are shown in [Table 9] and [Table 10],respectively.

TABLE 9 Sequence index Orthogonal sequences n_(oc) (n_(s)) [w(0) ∧w(N_(SF) ^(PUCCH) − 1)] 0 [+1 +1 +1 +1] 1 [+1 −1 +1 −1] 2 [+1 −1 −1 +1]

TABLE 10 Sequence index Orthogonal sequences n_(oc) (n_(s)) [w(0) ∧w(N_(SF) ^(PUCCH) − 1)] 0 [1 1 1] 1 [1 e^(j2π/3) e^(j4π/3)] 2 [1e^(j4π/3) e^(j2π/3)]

Orthogonal sequence (OC) [w(0)Λw(N_(RS) ^(PUCCH)−1)] for a referencesignal in PUCCH format 1/1a/1b is shown in [Table 11].

TABLE 11 Sequence index n _(oc)(n_(s)) Normal cyclic prefix Extendedcyclic prefix 0 [1 1 1] [1 1] 1 [1 e^(j2π/3) e^(j4π/3)] [1 −1] 2 [1e^(j4π/3) e^(j2π/3)] N/A

FIG. 8 shows PUCCH format 2/2a/2b in case of a normal cyclic prefix.And, FIG. 9 shows PUCCH format 2/2a/2b in case of an extended cyclicprefix.

Referring to FIG. 8 and FIG. 9, in case of a normal CP, a subframe isconstructed with 10 QPSK data symbols as well as RS symbol. Each QPSKsymbol is spread in a frequency domain by CS and is then mapped to acorresponding SC-FDMA symbol. SC-FDMA symbol level CS hopping may beapplied to randomize inter-cell interference. The RS may be multiplexedby CDM using a cyclic shift. For instance, assuming that the number ofavailable CSs is 12, 12 UEs may be multiplexed in the same PRB. Forinstance, assuming that the number of available CSs is 6, 6 UEs may bemultiplexed in the same PRB. In brief, a plurality of UEs in PUCCHformat 1/1a/1b and PUCCH format 2/2a/2b may be multiplexed by‘CS+OC+PRB’ and ‘CS+PRB’, respectively.

FIG. 10 is a diagram of ACK/NACK channelization for PUCCH formats 1a and1b. In particular, FIG. 10 corresponds to a case of ‘Δ_(shift)^(PUCCH)=2’

FIG. 11 is a diagram of channelization for a hybrid structure of PUCCHformat 1/1a/1b and PUCCH format 2/2a/2b.

Cyclic Shift (CS) hopping and OC remapping may be applicable in afollowing manner.

(1) Symbol-based cell-specific CS hopping for randomization ofinter-cell interference

(2) Slot level CS/OC remapping

-   -   1) For inter-cell interference randomization    -   2) Slot based access for mapping between ACK/NACK channel and        resource (k)

Meanwhile, resource n_(r) for PUCCH format 1/1a/1b may include thefollowing combinations.

(1) CS (=equal to DFT orthogonal code at symbol level) (n_(cs))

(2) OC (orthogonal cover at slot level) (n_(oc))

(3) Frequency RB (Resource Block) (n_(rb))

If indexes indicating CS, OC and RB are set to n_(cs), n_(oc), n_(rb),respectively, a representative index n_(r) may include n_(cs), n_(oc)and n_(rb). In this case, the n_(r) may meet the condition of‘n_(r)=(n_(cs), n_(oc), n_(rb))’.

The combination of CQI, PMI, RI, CQI and ACK/NACK may be deliveredthrough the PUCCH format 2/2a/2b. And, Reed Muller (RM) channel codingmay be applicable.

For instance, channel coding for UL (uplink) CQI in LTE system may bedescribed as follows. First of all, bitstreams a₀, a₁, a₂, a₃, . . . ,a_(A-1) may be coded using (20, A) RM code. In this case, a_(o) anda_(A-1) indicates MSB (Most Significant Bit) and LSB (Least SignificantBit), respectively. In case of an extended cyclic prefix, maximuminformation bits include 11 bits except a case that QI and ACK/NACK aresimultaneously transmitted. After coding has been performed with 20 bitsusing the RM code, QPSK modulation may be applied. Before the BPSKmodulation, coded bits may be scrambled.

[Table 12] shows a basic sequence for (20, A) code.

TABLE 12 i M_(i,0) M_(i,1) M_(i,2) M_(i,3) M_(i,4) M_(i,5) M_(i,6)M_(i,7) M_(i,8) M_(i,9) M_(i,10) M_(i,11) M_(i,12) 0 1 1 0 0 0 0 0 0 0 01 1 0 1 1 1 1 0 0 0 0 0 0 1 1 1 0 2 1 0 0 1 0 0 1 0 1 1 1 1 1 3 1 0 1 10 0 0 0 1 0 1 1 1 4 1 1 1 1 0 0 0 1 0 0 1 1 1 5 1 1 0 0 1 0 1 1 1 0 1 11 6 1 0 1 0 1 0 1 0 1 1 1 1 1 7 1 0 0 1 1 0 0 1 1 0 1 1 1 8 1 1 0 1 1 00 1 0 1 1 1 1 9 1 0 1 1 1 0 1 0 0 1 1 1 1 10 1 0 1 0 0 1 1 1 0 1 1 1 111 1 1 1 0 0 1 1 0 1 0 1 1 1 12 1 0 0 1 0 1 0 1 1 1 1 1 1 13 1 1 0 1 0 10 1 0 1 1 1 1 14 1 0 0 0 1 1 0 1 0 0 1 0 1 15 1 1 0 0 1 1 1 1 0 1 1 0 116 1 1 1 0 1 1 1 0 0 1 0 1 1 17 1 0 0 1 1 1 0 0 1 0 0 1 1 18 1 1 0 1 1 11 1 0 0 0 0 0 19 1 0 0 0 0 1 1 0 0 0 0 0 0

Channel coding bits b₀, b₁, b₂, b₃, . . . , b_(B-1) may be generated by[Equation 1].

$\begin{matrix}{b_{i} = {\sum\limits_{n - 0}^{A - 1}{\left( {a_{n} \cdot M_{i,n}} \right)\mspace{11mu} {mod}\mspace{11mu} 2}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In [Equation 3], ‘i=0, 1, 2, . . . , B-1’ is met.

In case of wideband repots, a bandwidth of Uplink Control Information)field for CQI/PMI can be represented as Tables 8 to 10 in the following.

[Table 13] shows UCI field for broadband report (single antenna port,transmit diversity) or open loop spatial multiplexing PDSCH CQIfeedback.

TABLE 13 Field Bandwidth Broadband CQI 4

[Table 14] shows UL control information (UCI) field for CQI and PMIfeedback in case of wideband reports (closed loop spatial multiplexingPDSCH transmission).

TABLE 14 Bandwidth 2 antenna ports 4 antenna ports Field rank = 1 rank =2 rank = 1 Rank >1 Wideband CQI 4 4 4 4 Spatial differential CQI 0 3 0 3Precoding Matrix 2 1 4 4 Indication

[Table 15] shows UL Control Information (UCI) field for RI feedback incase of wideband reports.

TABLE 15 Bit widths 4 antenna ports 2 Max. 2 Max. 4 Field antenna portslayers layers Rank 1 1 2 Indication

FIG. 12 is a diagram for PRB allocation. Referring to FIG. 20, PRB maybe usable for PUCCH transmission in a slot n_(s).

2. Carrier Aggregation (CA) Environment

2.1 CA Overview

A 3GPP LTE system (conforming to Rel-8 or Rel-9) (hereinafter, referredto as an LTE system) uses Multi-Carrier Modulation (MCM) in which asingle Component Carrier (CC) is divided into a plurality of bands. Incontrast, a 3GPP LTE-A system (hereinafter, referred to an LTE-A system)may use CA by aggregating one or more CCs to support a broader systembandwidth than the LTE system. The term CA is interchangeably used withcarrier combining, multi-CC environment, or multi-carrier environment.

In the present disclosure, multi-carrier means CA (or carriercombining). Herein, CA covers aggregation of contiguous carriers andaggregation of non-contiguous carriers. The number of aggregated CCs maybe different for a DL and a UL. If the number of DL CCs is equal to thenumber of UL CCs, this is called symmetric aggregation. If the number ofDL CCs is different from the number of UL CCs, this is called asymmetricaggregation. The term CA is interchangeable with carrier combining,bandwidth aggregation, spectrum aggregation, etc.

The LTE-A system aims to support a bandwidth of up to 100 MHz byaggregating two or more CCs, that is, by CA. To guarantee backwardcompatibility with a legacy IMT system, each of one or more carriers,which has a smaller bandwidth than a target bandwidth, may be limited toa bandwidth used in the legacy system.

For example, the legacy 3GPP LTE system supports bandwidths {1.4, 3, 5,10, 15, and 20 MHz} and the 3GPP LTE-A system may support a broaderbandwidth than 20 MHz using these LTE bandwidths. A CA system of thepresent disclosure may support CA by defining a new bandwidthirrespective of the bandwidths used in the legacy system.

There are two types of CA, intra-band CA and inter-band CA. Intra-bandCA means that a plurality of DL CCs and/or UL CCs are successive oradjacent in frequency. In other words, the carrier frequencies of the DLCCs and/or UL CCs are positioned in the same band. On the other hand, anenvironment where CCs are far away from each other in frequency may becalled inter-band CA. In other words, the carrier frequencies of aplurality of DL CCs and/or UL CCs are positioned in different bands. Inthis case, a UE may use a plurality of Radio Frequency (RF) ends toconduct communication in a CA environment.

The LTE-A system adopts the concept of cell to manage radio resources.The above-described CA environment may be referred to as a multi-cellenvironment. A cell is defined as a pair of DL and UL CCs, although theUL resources are not mandatory. Accordingly, a cell may be configuredwith DL resources alone or DL and UL resources.

For example, if one serving cell is configured for a specific UE, the UEmay have one DL CC and one UL CC. If two or more serving cells areconfigured for the UE, the UE may have as many DL CCs as the number ofthe serving cells and as many UL CCs as or fewer UL CCs than the numberof the serving cells, or vice versa. That is, if a plurality of servingcells are configured for the UE, a CA environment using more UL CCs thanDL CCs may also be supported.

CA may be regarded as aggregation of two or more cells having differentcarrier frequencies (center frequencies). Herein, the term ‘cell’ shouldbe distinguished from ‘cell’ as a geographical area covered by an eNB.Hereinafter, intra-band CA is referred to as intra-band multi-cell andinter-band CA is referred to as inter-band multi-cell.

In the LTE-A system, a Primacy Cell (PCell) and a Secondary Cell (SCell)are defined. A PCell and an SCell may be used as serving cells. For a UEin RRC_CONNECTED state, if CA is not configured for the UE or the UEdoes not support CA, a single serving cell including only a PCell existsfor the UE. On the contrary, if the UE is in RRC_CONNECTED state and CAis configured for the UE, one or more serving cells may exist for theUE, including a PCell and one or more SCells.

Serving cells (PCell and SCell) may be configured by an RRC parameter. Aphysical-layer ID of a cell, PhysCellId is an integer value ranging from0 to 503. A short ID of an SCell, SCellIndex is an integer value rangingfrom 1 to 7. A short ID of a serving cell (PCell or SCell),ServeCellIndex is an integer value ranging from 1 to 7. IfServeCellIndex is 0, this indicates a PCell and the values ofServeCellIndex for SCells are pre-assigned. That is, the smallest cellID (or cell index) of ServeCellIndex indicates a PCell.

A PCell refers to a cell operating in a primary frequency (or a primaryCC). A UE may use a PCell for initial connection establishment orconnection reestablishment. The PCell may be a cell indicated duringhandover. In addition, the PCell is a cell responsible forcontrol-related communication among serving cells configured in a CAenvironment. That is, PUCCH allocation and transmission for the UE maytake place only in the PCell. In addition, the UE may use only the PCellin acquiring system information or changing a monitoring procedure. AnEvolved Universal Terrestrial Radio Access Network (E-UTRAN) may changeonly a PCell for a handover procedure by a higher layerRRCConnectionReconfiguraiton message including mobilityControlInfo to aUE supporting CA.

An SCell may refer to a cell operating in a secondary frequency (or asecondary CC). Although only one PCell is allocated to a specific UE,one or more SCells may be allocated to the UE. An SCell may beconfigured after RRC connection establishment and may be used to provideadditional radio resources. There is no PUCCH in cells other than aPCell, that is, in SCells among serving cells configured in the CAenvironment.

When the E-UTRAN adds an SCell to a UE supporting CA, the E-UTRAN maytransmit all system information related to operations of related cellsin RRC_CONNECTED state to the UE by dedicated signaling. Changing systeminformation may be controlled by releasing and adding a related SCell.Herein, a higher layer RRCConnectionReconfiguration message may be used.The E-UTRAN may transmit a dedicated signal having a different parameterfor each cell rather than it broadcasts in a related SCell.

After an initial security activation procedure starts, the E-UTRAN mayconfigure a network including one or more SCells by adding the SCells toa PCell initially configured during a connection establishmentprocedure. In the CA environment, each of a PCell and an SCell mayoperate as a CC. Hereinbelow, a Primary CC (PCC) and a PCell may be usedin the same meaning and a Secondary CC (SCC) and an SCell may be used inthe same meaning in embodiments of the present disclosure.

FIG. 13, including views (a) and (b), illustrates an example of CCs andCA in the LTE-A system, which are used in embodiments of the presentdisclosure.

FIG. 13(a) illustrates a single carrier structure in the LTE system.There are a DL CC and a UL CC and one CC may have a frequency range of20 MHz.

FIG. 13(b) illustrates a CA structure in the LTE-A system. In theillustrated case of FIG. 13(b), three CCs each having 20 MHz areaggregated. While three DL CCs and three UL CCs are configured, thenumbers of DL CCs and UL CCs are not limited. In CA, a UE may monitorthree CCs simultaneously, receive a DL signal/DL data in the three CCs,and transmit a UL signal/UL data in the three CCs.

If a specific cell manages N DL CCs, the network may allocate M (M≤N) DLCCs to a UE. The UE may monitor only the M DL CCs and receive a DLsignal in the M DL CCs. The network may prioritize L (L≤M≤N) DL CCs andallocate a main DL CC to the UE. In this case, the UE should monitor theL DL CCs. The same thing may apply to UL transmission.

The linkage between the carrier frequencies of DL resources (or DL CCs)and the carrier frequencies of UL resources (or UL CCs) may be indicatedby a higher layer message such as an RRC message or by systeminformation. For example, a set of DL resources and UL resources may beconfigured based on linkage indicated by System Information Block Type 2(SIB2). Specifically, DL-UL linkage may refer to a mapping relationshipbetween a DL CC carrying a PDCCH with a UL grant and a UL CC using theUL grant, or a mapping relationship between a DL CC (or a UL CC)carrying HARQ data and a UL CC (or a DL CC) carrying an HARQ ACK/NACKsignal.

2.2 Cross Carrier Scheduling

Two scheduling schemes, self-scheduling and cross carrier scheduling aredefined for a CA system, from the perspective of carriers or servingcells. Cross carrier scheduling may be called cross CC scheduling orcross cell scheduling.

In self-scheduling, a PDCCH (carrying a DL grant) and a PDSCH aretransmitted in the same DL CC or a PUSCH is transmitted in a UL CClinked to a DL CC in which a PDCCH (carrying a UL grant) is received.

In cross carrier scheduling, a PDCCH (carrying a DL grant) and a PDSCHare transmitted in different DL CCs or a PUSCH is transmitted in a UL CCother than a UL CC linked to a DL CC in which a PDCCH (carrying a ULgrant) is received.

Cross carrier scheduling may be activated or deactivated UE-specificallyand indicated to each UE semi-statically by higher layer signaling (e.g.RRC signaling).

If cross carrier scheduling is activated, a Carrier Indicator Field(CIF) is required in a PDCCH to indicate a DL/UL CC in which aPDSCH/PUSCH indicated by the PDCCH is to be transmitted. For example,the PDCCH may allocate PDSCH resources or PUSCH resources to one of aplurality of CCs by the CIF. That is, when a PDCCH of a DL CC allocatesPDSCH or PUSCH resources to one of aggregated DL/UL CCs, a CIF is set inthe PDCCH. In this case, the DCI formats of LTE Release-8 may beextended according to the CIF. The CIF may be fixed to three bits andthe position of the CIF may be fixed irrespective of a DCI format size.In addition, the LTE Release-8 PDCCH structure (the same coding andresource mapping based on the same CCEs) may be reused.

On the other hand, if a PDCCH transmitted in a DL CC allocates PDSCHresources of the same DL CC or allocates PUSCH resources in a single ULCC linked to the DL CC, a CIF is not set in the PDCCH. In this case, theLTE Release-8 PDCCH structure (the same coding and resource mappingbased on the same CCEs) may be used.

If cross carrier scheduling is available, a UE needs to monitor aplurality of PDCCHs for DCI in the control region of a monitoring CCaccording to the transmission mode and/or bandwidth of each CC.Accordingly, an appropriate SS configuration and PDCCH monitoring areneeded for the purpose.

In the CA system, a UE DL CC set is a set of DL CCs scheduled for a UEto receive a PDSCH, and a UE UL CC set is a set of UL CCs scheduled fora UE to transmit a PUSCH. A PDCCH monitoring set is a set of one or moreDL CCs in which a PDCCH is monitored. The PDCCH monitoring set may beidentical to the UE DL CC set or may be a subset of the UE DL CC set.The PDCCH monitoring set may include at least one of the DL CCs of theUE DL CC set. Or the PDCCH monitoring set may be defined irrespective ofthe UE DL CC set. DL CCs included in the PDCCH monitoring set may beconfigured to always enable self-scheduling for UL CCs linked to the DLCCs. The UE DL CC set, the UE UL CC set, and the PDCCH monitoring setmay be configured UE-specifically, UE group-specifically, orcell-specifically.

If cross carrier scheduling is deactivated, this implies that the PDCCHmonitoring set is always identical to the UE DL CC set. In this case,there is no need for signaling the PDCCH monitoring set. However, ifcross carrier scheduling is activated, the PDCCH monitoring set may bedefined within the UE DL CC set. That is, the eNB transmits a PDCCH onlyin the PDCCH monitoring set to schedule a PDSCH or PUSCH for the UE.

FIG. 14 illustrates a cross carrier-scheduled subframe structure in theLTE-A system, which is used in embodiments of the present disclosure.

Referring to FIG. 14, three DL CCs are aggregated for a DL subframe forLTE-A UEs. DL CC ‘A’ is configured as a PDCCH monitoring DL CC. If a CIFis not used, each DL CC may deliver a PDCCH that schedules a PDSCH inthe same DL CC without a CIF. On the other hand, if the CIF is used byhigher layer signaling, only DL CC ‘A’ may carry a PDCCH that schedulesa PDSCH in the same DL CC ‘A’ or another CC. Herein, no PDCCH istransmitted in DL CC ‘B’ and DL CC ‘C’ that are not configured as PDCCHmonitoring DL CCs.

FIG. 15 is conceptual diagram illustrating a construction of servingcells according to cross-carrier scheduling.

Referring to FIG. 15, an eNB (or BS) and/or UEs for use in a radioaccess system supporting carrier aggregation (CA) may include one ormore serving cells. In FIG. 8, the eNB can support a total of fourserving cells (cells A, B, C and D). It is assumed that UE A may includeCells (A, B, C), UE B may include Cells (B, C, D), and UE C may includeCell B. In this case, at least one of cells of each UE may be composedof P Cell. In this case, P Cell is always activated, and S Cell may beactivated or deactivated by the eNB and/or UE.

The cells shown in FIG. 15 may be configured per UE. The above-mentionedcells selected from among cells of the eNB, cell addition may be appliedto carrier aggregation (CA) on the basis of a measurement report messagereceived from the UE. The configured cell may reserve resources forACK/NACK message transmission in association with PDSCH signaltransmission. The activated cell is configured to actually transmit aPDSCH signal and/or a PUSCH signal from among the configured cells, andis configured to transmit CSI reporting and Sounding Reference Signal(SRS) transmission. The deactivated cell is configured not totransmit/receive PDSCH/PUSCH signals by an eNB command or a timeroperation, and CRS reporting and SRS transmission are interrupted.

2.3 CA PUCCH (Carrier Aggregation Physical Uplink Control Channel)

In a wireless communication system supportive of carrier aggregation,PUCCH format for feeding back UCI (e.g., multi-ACK/NACK bit) can bedefined. For clarity of the following description, such PUCCH formatshall be named CA PUCCH format.

FIG. 16 is a diagram for one example of a signal processing process ofCA PUCCH.

Referring to FIG. 16, a channel coding block generates coding bits(e.g., encoded bits, coded bits, etc.) (or codeword) b_0, b_1, . . . andb_N−1 by channel-coding information bits a_0, a_1, . . . and a_M−1(e.g., multiple ACK/NACK bits). In this case, the M indicates a size ofinformation bits and the N indicates a size of the coding bits. Theinformation bits may include multiple ACK/NACK for UL controlinformation (UCI), e.g., a plurality of data (or PDSCH) received via aplurality of DL CCS. In this case, the information bits a_0, a_1, . . .a_M−1 may be joint-coded irrespective of type/number/size of the UCIconfiguring the information bits. For instance, in case that informationbits include multiple ACK/NACK for a plurality of DL CCs, channel codingmay not be performed per DL CC or individual ACK/NACK bit but may beperformed on all bit information, from which a single codeword may begenerated. And, channel coding is non-limited by this. Moreover, thechannel coding may include one of simplex repetition, simplex coding,Reed Muller (RM) coding, punctured RM coding, Tail-Biting ConvolutionalCoding (TBCC), Low-Density Parity-Check (LDPC), turbo coding and thelike. Besides, coding bits may be rate-matched in consideration of amodulation order and a resource size (not shown in the drawing). A ratematching function may be included as a part of the channel coding blockor may be performed via a separate function block.

A modulator generates modulated symbols c_0, c_1 . . . c_L-1 bymodulating coding bits b_0, b_1 . . . b_N-1. In this case, the Lindicates a size of modulated symbol. This modulation scheme may beperformed in a manner of modifying a size and phase of a transmissionsignal. For instance, the modulation scheme may include one of n-aryPhase Shift Keying (n-PSK), n-ary Quadrature Amplitude Modulation(n-QAM) and the like, where n is an integer equal to or greater than 2.In particular, the modulation scheme may include one of Binary PhaseShift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 8-PSK, QAM,16-QAM, 64-QAM and the like.

A divider divides the modulated symbols c_0, c_1 c_L-1 to slots,respectively. A sequence/pattern/scheme for dividing the modulatedsymbols to the slots may be specially non-limited. For instance, thedivider may be able to divide the modulated symbols to the correspondingslots in order from a head to tail (Localized scheme). In doing so, asshown in the drawing, the modulated symbols c_0, c_1 . . . c_L/2−1 maybe divided to the slot 0 and the modulated symbols c_L/2, c_L/2+1 . . .c_L-1 may be divided to the slot 1. Moreover, the modulated symbols maybe divided to the corresponding slots, respectively, by interleaving orpermutation. For instance, the even-numbered modulated symbol may bedivided to the slot 0, while the odd-numbered modulated symbol may bedivided to the slot 1. The modulation scheme and the dividing scheme maybe switched to each other in order.

A DFT precoder may perform DFT precoding (e.g., 12-point DFT) on themodulated symbols divided to the corresponding slots to generate asingle carrier waveform. Referring to the drawing, the modulated symbolsc_0, c_1 . . . c_L/2−1 divided to the corresponding slot 0 may beDFT-precoded into DFT symbols d_0, d_1 . . . d_L/2−1, and the modulatedsymbols c_L/2, c_L/2+1 . . . c_L-1 divided to the slot 1 may beDFT-precoded into DFT symbols d_L/2, d_L/2+1 . . . d_L-1. Moreover, theDFT precoding may be replaced by another linear operation (e.g., Walshprecoding) corresponding thereto.

A spreading block may spread the DFT-performed signal at SC-FDMA symbolslevel (e.g., time domain). The time-domain spreading at the SC-FDMAlevel may be performed using a spreading code (sequence). The spreadingcode may include pseudo orthogonal code and orthogonal code. The pseudoorthogonal code may include PN (pseudo noise) code, by which the pseudoorthogonal code may be non-limited. The orthogonal code may includeWalsh code and DFT code, by which the orthogonal code may benon-limited. The orthogonal code (OC) may be interchangeably used withone of an orthogonal sequence, an OC and an OCC. In this specification,for example, the orthogonal code may be mainly described as arepresentative example of the spreading code for clarity and convenienceof the following description. Optionally, the orthogonal code may besubstituted with the pseudo orthogonal code. A maximum value of aspreading code size (or a Spreading Factor (SF)) may be limited by thenumber of SC-FDAM symbols used for control information transmission. Forexample, in case that 5 SC-FDMA symbols are used in one slot for controlinformation transmission, orthogonal codes (or pseudo orthogonal codes)w0, w1, w2, w3 and w4 of length 5 may be used per slot. The SF may meana spreading degree of the control information and may be associated witha multiplexing order or an antenna multiplexing order of a UE. The SFmay be variable like 1, 2, 3, 4, 5 . . . depending on a requirement of asystem. The SF may be defined in advance between a base station and aUE. And, the SF may be notified to a UE via DCI or RRC signaling.

The signal generated through the above-described process may be mappedto subcarrier within the PRB and may be then transformed into atime-domain signal through IFFT. CP may be attached to the time-domainsignal. The generated SC-FDMA symbol may be then transmitted through anRF stage.

3. Method for Feeding Back Channel State Information (CSI)

3.1 Channel State Information (CSI)

First of all, in the 3GPP LTE system, when a DL reception entity (e.g.,a UE) is connected to a DL transmission entity (e.g., a BS), the DLreception entity performs measurement on a Reference Signal ReceivedPower (RSRP) of a reference signal transmitted in DL, a quality of areference signal (Reference Signal Received Quality (RSRQ)) and the likeat a random time and is then able to make a periodic or even-triggeredreport of a corresponding measurement result to the base station.

Each UE reports a DL channel information in accordance with a DL channelstatus via uplink. A base station is then able to determinetime/frequency resources, Modulation and Coding Scheme (MCS) and thelike appropriate for a data transmission to each UE using the DL channelinformation received from the each UE.

Such CSI may include Channel Quality Indication (CQI), Precoding MatrixIndicator (PMIC), Precoder Type Indication (PTI) and/or Rank Indication(RI). In particular, the CSI may be transmitted entirely or partiallydepending on a transmission mode of each UE. CQI is determined based ona received signal quality of a UE, which may be generally determined onthe basis of a measurement of a DL reference signal. In doing so, a CQIvalue actually delivered to a base station may correspond to an MCScapable of providing maximum performance by maintaining a Block ErrorRate (BLER) under 10% in the received signal quality measured by a UE.

This channel information reporting may be classified into a periodicreport transmitted periodically and an aperiodic report transmitted inresponse to a request made by a base station.

In case of the aperiodic report, it is set for each UE by a 1-bitrequest bit (CQI request bit) contained in UL scheduling informationdownloaded to a UE by a base station. Having received this information,each UE is then able to deliver channel information to the base stationvia a physical uplink shared channel (PUSCH) in consideration of itstransmission mode. And, it may set RI and CQI/PMI not to be transmittedon the same PUSCH.

In case of the periodic report, a period for transmitting channelinformation via an upper layer signal, an offset in the correspondingperiod and the like are signaled to each UE by subframe unit and channelinformation in consideration of a transmission mode of each UE may bedelivered to a base station via a PUCCH in accordance with a determinedperiod. In case that data transmitted in uplink simultaneously exists ina subframe in which channel information is transmitted by a determinedperiod, the corresponding channel information may be transmittedtogether with the data not on the PUCCH but on a PUSCH. In case of theperiodic report via PUCCH, bits (e.g., 11 bits) limited further thanthose of the PUSCH may be used. RI and CQI/PMI may be transmitted on thesame PUSCH.

In case that contention occurs between the periodic report and theaperiodic report in the same subframe, only the aperiodic report can beperformed.

In calculating Wideband CQI/PMI, a most recently transmitted RI may beusable. RI in a PUCCH CSI report mode is independent from RI in a PUSCHCSI report mode. The RI in the PUSCH CSI report mode is valid forCQI/PMI in the corresponding PUSCH CSI report mode only.

[Table 16] is provided to describe CSI feedback type transmitted onPUCCH and PUCCH CSI report mode.

TABLE 16 PMI Feedback Type No PMI (OL, TD, single-antenna) Single PMI(CL) CQI Wideband Mode 1-0 Mode 1-1 Feedback RI (only for Open-Loop SM)RI Type One Wideband CQI (4 bit) Wideband CQI (4 bit) when RI>1, CQI offirst codeword Wideband spatial CQI (3 bit) for RI>1 Wideband PMI (4bit) UE Mode 2-0 Mode 2-1 Selected RI (only for Open-Loop SM) RIWideband CQI (4 bit) Wideband CQI (4 bit) Best-1 CQI (4 bit) in each BPWideband spatial CQI (3 bit) for RI>1 Best-1 indicator(L-bit label)Wideband PMI (4 bit) when RI>1, CQI of first codeword Best-1 CQI (4 bit)1 in each BP Best-1 spatial CQI (3 bit) for RI>1 Best-1 indicator (L-bitlabel)

Referring to [Table 16], in the periodic report of channel information,there are 4 kinds of reporting modes (mode 1-0, mode 1-2, mode 2-0 andmode 2-1) in accordance with CQI and PMI feedback types.

CQI can be classified into WideBand (WB) CQI and SubBand (SB) CQI inaccordance with CQI feedback type and PMI can be classified into No PMIor Single PMI in accordance with a presence or non-presence of PMItransmission. In [Table 11], No PMI corresponds to a case of Open-Loop(OL), Transmit Diversity (TD) and single-antenna, while Single PMIcorresponds to a case of Closed-Loop (CL).

The mode 1-0 corresponds to a case that WB CQI is transmitted in theabsence of PMI transmission. In this case, RI is transmitted only incase of OL Spatial Multiplexing (SM) and one WB CQI represented as 4bits can be transmitted. If RI is greater than 1, CQI for a 1^(st)codeword can be transmitted.

The mode 1-1 corresponds to a case that a single PMI and WB CQI aretransmitted. In this case, 4-bit WB CQI and 4-bit WB PMI can betransmitted together with RI transmission. Additionally, if RI isgreater than 1, 3-bit WB spatial differential CQI can be transmitted. In2-codeword transmission, the WB spatial differential CQI may indicate adifference value between a WB CQI index for codeword 1 and a WB CQIindex for codeword 2. The difference value in-between may have a valueselected from a set {−4, −3, −2, −1, 0, 1, 2, 3} and can be representedas 3 bits.

The mode 2-0 corresponds to a case that CQI on a UE-selected band istransmitted in the absence of PMI transmission. In this case, RI istransmitted only in case of open-loop SM and a WB CQI represented as 4bits may be transmitted. A best CQI (best-1) is transmitted on eachBandwidth Part (BP) and the best-1 CQI may be represented as 4 bits.And, an L-bit indicator indicating the best-1 may be transmittedtogether. If the RI is greater than 1, a CQI for a 1^(st) codeword canbe transmitted.

And, the mode 2-1 corresponds to a case that a single PMI and a CQI on aUE-selected band are transmitted. In this case, together with RItransmission, 4-bit WB CQI, 3-bit WB spiral differential CQI and 4-bitWB PMI can be transmitted. Additionally, 4-bit best-1 CQI is transmittedon each BP and L-bit best-1 indicator can be transmitted together.Additionally, if RI is greater than 1, 3-bit best-1 spatial differentialCQI can be transmitted. In 2-codeword transmission, it may indicate adifference value between a best-1 CQI index of codeword 1 and a best-1CQI index of codeword 2.

For the transmission modes, periodic PUCCH CSI report modes aresupported as follows.

1) Transmission mode 1: Modes 1-0 and 2-0

2) Transmission mode 2: Modes 1-0 and 2-0

3) Transmission mode 3: Modes 1-0 and 2-0

4) Transmission mode 4: Modes 1-1 and 2-1

5) Transmission mode 5: Modes 1-1 and 2-1

6) Transmission mode 6: Modes 1-1 and 2-1

7) Transmission mode 7: Modes 1-0 and 2-0

8) Transmission mode 8: Modes 1-1 and 2-1 if a UE is set to make aPMI/RI reporting, or Modes 1-0 and 2-0 if a UE is set not to make aPMI/RI reporting

9) Transmission mode 9: Modes 1-1 and 2-1 if a UE is set to make aPMI/RI reporting and the number of CSI-RS ports is greater than 1, orModes 1-0 and 2-0 if a UE is set not to make a PMI/RI reporting and thenumber of CSI-RS port(s) is equal to 1.

The periodic PUCCH CSIU reporting mode in each serving cell is set byupper layer signaling. And, the mode 1-1 is set to either submode 1 orsubmode 2 by an upper layer signaling using a parameter‘PUCCH_format1-1_CSI_reporting_mode’.

A CQI reporting in a specific subframe of a specific serving cell in aUE-selected SB CQI means a measurement of at least one channel state ofa BP corresponding to a portion of a bandwidth of a serving cell. Anindex is given to the bandwidth part in a frequency increasing orderstarting with a lowest frequency without an increment of a bandwidth.

3.2 CSI Feedback Method

In an LTE system, an open-loop MIMO scheme operated without channelinformation and a closed-loop MIMO scheme operated based on channelinformation are used. Especially, according to the closed-loop MIMOscheme, each of a transmitter and a receiver may be able to performbeamforming based on channel information (e.g., CSI) to obtain amultiplexing gain of MIMO antennas. To obtain CSI, the eNB allocates aPUCCH or a PUSCH to the UE and instructs the UE to feed back CSI of adownlink channel.

CSI includes RI information, Precoding Matrix Indicator (PMI)information, and CQI information. First, RI indicates rank informationof a channel and means the number of data streams that can be receivedby the UE via the same frequency-time resource. Since RI is dominantlydetermined by long-term fading of a channel, this may be generally fedback from the UE to the eNB at a cycle longer than that of PMI or CQI.PMI is a value to which the spatial characteristic of a channel isreflected. PMI indicates a precoding index of the eNB preferred by theUE based on a metric of Signal-to-Interference plus Noise Ratio (SINR).Lastly, CQI is information indicating the strength of a channel andgenerally indicates a reception SINR obtainable when the eNB uses PMI.

In an advanced system such as an LTE-A system, a method for obtainingadditional multi-user diversity using Multi-User MIMO (MU-MIMO) wasadded. Higher accuracy is required in terms of channel feedback. Sincean interference channel exists between UEs multiplexed in an antennadomain in MU-MIMO, the accuracy of CSI may significantly affectinterference with other multiplexed UEs as well as a UE for performingfeedback. Accordingly, in an LTE-A system, in order to increase accuracyof a feedback channel, a final PMI has been determined to be separatelydesigned as a long-term and/or wideband PMI, W1, and a short-term and/orsubband PMI, W2.

The eNB can transform a codebook using a long-term covariance matrix ofa channel as shown in Equation 4 below as an example of a hierarchicalcodebook transformation method configuring one final PMI from two typesof channel information such as W1 and W2.

W=norm(W1W2)

In Equation 4, W1 (that is, long-term PMI) and W2 (that is, short-termPMI) denote codewords of a codebook generated in order to reflectchannel information, W denotes a codeword of a final transformedcodebook, and norm (A) denotes a matrix obtained by normalizing the normof each column of a matrix A to 1.

In Equation 4, the structures of W1 and W2 are shown in Equation 5below.

$\begin{matrix}{{{W\; 1(i)} = \begin{bmatrix}X_{i} & 0 \\0 & X_{i}\end{bmatrix}},} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

where X_(i) is Nt/2 by M matrix.

${W\; 2(j)} = {\overset{\overset{rcolumns}{({6\mspace{31mu} 4\mspace{31mu} 4\mspace{31mu} 4\mspace{31mu} 7\mspace{31mu} 4\mspace{31mu} 4\mspace{31mu} 4\mspace{31mu} 8})}}{\begin{bmatrix}e_{M}^{k} & e_{M}^{l} & \; & e_{M}^{m} \\{\alpha_{j}e_{M}^{k}} & {\beta_{j}e_{m}^{l}} & \ldots & {\gamma_{j}e_{M}^{m}}\end{bmatrix}}\mspace{14mu} \left( {{{if}\mspace{14mu} {rank}} = r} \right)}$

where 1≤k,l,m≤M and k,l,m are integer.

The codeword structures of W1 and W2 shown in Equation 5 are designed byreflecting correlation characteristics of the channel generated when across-polarized antenna is used and a gap between antennas is narrow(e.g., a distance between adjacent antennas is equal to or less thanhalf a signal wavelength).

The cross-polarized antennas may be divided into a horizontal antennagroup and a vertical antenna group. At this time, each antenna group hasa uniform linear array (ULA) antenna property and two antenna groups areco-located. Accordingly, the correlations between antennas in each grouphave the same linear phase increment property and the correlationbetween the antenna groups has a phase rotation property.

Since a codebook is a value obtained by quantizing radio channels, acodebook may be designed by reflecting the characteristics of a channelcorresponding to a source without change. Equation 6 below shows anexample of a rank-1 codeword designed using the structures of Equations4 and 5, for convenience of description. Referring to Equation 6, it canbe seen that such channel properties are reflected to the codewordsatisfying Equation 4.

$\begin{matrix}{{W\; 1(i)*W\; 2(j)} = \begin{bmatrix}{X_{i}(k)} \\{\alpha_{j}{X_{i}(k)}}\end{bmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

In Equation 6, a codeword is expressed as an N_(t) (that is, the numberof transmit antennas)×1 vector. At this time, Equation 6 is composed ofan upper vector X_(i)(k) and a lower vector α_(j)X_(i)(k), whichrespectively represent the correlation characteristics of the horizontaland vertical antenna groups. At this time, X_(i)(k) is expressed as avector having the linear phase increment property by reflecting thecorrelation characteristics between antenna groups. A representativeexample thereof includes a Discrete Fourier Transform (DFT) matrix.

In addition, higher channel accuracy is necessary for CoMP. For example,CoMP joint transmission (JP) may be theoretically regarded as a MIMOsystem in which antennas are geographically distributed, because severaleNBs cooperatively transmit the same data to a specific UE. That is,even when MU-MIMO is implemented in JT, very high channel accuracy isrequired to avoid interference between UEs scheduled together, similarlyto single cell MU-MIMO operation. Even in CoMP Coordinated Beamforming(CB), precise channel information is required to avoid interference witha serving cell caused by a neighbor cell.

3.3 UE Operation for CSI Reporting

Time and frequency resources used by the UE to report CSI including CQI,PMI, PTI and/or RI are scheduled by the eNB. For SM, the UE shalldetermine RI corresponding to the number of transmission layers. Fortransmit diversity, the UE sets RI to 1.

A UE in transmission mode 8 or 9 is configured with or without PMI/RIreporting by a higher layer parameter pmi-RI-report. A UE is configuredwith resource-restricted CSI measurements if subframe sets C_(CSI,0) andC_(CSI,1) are configured by a higher layer.

When a UE is configured with one or more serving cells, the UE performsa CSI reporting only for activated serving cells. When the UE is notconfigured for simultaneous PUSCH and PUCCH transmission, the UEperiodically performs CSI reporting on the PUCCH in the subframe with noPUSCH allocation. When the UE is not configured for simultaneous PUSCHand PUCCH transmission, the UE performs periodic CSI reporting in asubframe to which the PUSCH of a serving cell having a smallest servingcell index ServCellIndex is allocated. At this time, the UE uses thesame format as the PUCCH-based periodic CSI reporting format on thePUSCH. Under a predetermined condition, the UE transmits periodic CSIreporting on the PUSCH. For example, for aperiodic CQI/PMI reporting, RIreporting is transmitted only when the configured CSI feedback typesupports RI reporting.

In addition, even when the UE periodically performs CSI reporting, theUE may aperiodically perform CSI reporting when UL grant, in which a CSIrequest field is set, is received from the eNB.

3.3.1 Aperiodic CSI Reporting Using PUSCH

The UE performs aperiodic CSI reporting using the PUSCH in a subframen+k, upon receiving an uplink DCI format (that is, UL grant) or randomaccess response grant, in which a CSI request field is set, in asubframe n of a serving cell c. When the CSI request field has 1 bit andis set to “1”, the CSI reporting request is triggered for the servingcell c. When the CSI request field has 2 bits, the CSI reporting requestis triggered according to [Table 17] below.

TABLE 17 Value of CSI request field Description ‘00’ No aperiodic CSIreport is triggered ‘01’ Aperiodic CSI report is triggered for servingcell c ‘10’ Aperiodic CSI report is triggered for a 1^(st) set ofserving cells configured by higher layers ‘11’ Aperiodic CSI report istriggered for a 2^(nd) set of serving cells configured by higher layers

In [Table 17], the CSI request field set to “00” indicates that noaperiodic CSI report is triggered, “01” indicates that the aperiodic CSIreport is triggered for the serving cell c, “10” indicates that theaperiodic CSI report is triggered for a first set of serving cellsconfigured by higher layers, and “11” indicates that the aperiodic CSIreport is triggered for a second set of serving cells configured byhigher layers.

A UE is not expected to receive more than one aperiodic CSI reportrequest for a given subframe.

[Table 18] below lists reporting modes for CSI transmission on a PUSCH.

TABLE 18 PMI feedback type No Single Multiple PMI PMI PMI PUSCH WidebandMode CQI (wideband 1-2 feedback CQI) type UE Selected Mode Mode (subband2-0 2-2 CQI) Higher Mode Mode Layer-configured 3-0 3-1 (subband CQI)

Transmission modes listed in [Table 18] are selected by a higher layer,and a CQI, a PMI, and an RI are transmitted in the same PUSCH subframe.A detailed description will be given of each reporting mode.

1-1) Mode 1-2

A UE selects a precoding matrix for each subband on the assumption thatdata is transmitted only in the subband. The UE generates CQI on theassumption of a previously selected precoding matrix for a system bandor all bands (set S) indicated by the higher layer. Further, the UEtransmits the CQI and a PMI for each subband. Herein, the size of eachsubband may vary with the size of the system band.

1-2) Mode 2-0

The UE selects M preferred subbands for a system band or a band (set S)indicated by the higher layer. The UE generates one CQI on theassumption that data is transmitted in the selected M subbands. The UEadditionally generates one wideband CQI for the system band or the setS. If there are a plurality of codewords for the selected M subbands,the UE defines a CQI for each codeword as a differential value. Herein,differential CQIs are set to values obtained by subtracting a widebandCQI index from indexes corresponding to CQIs for the selected Msubbands.

The UE transmits information about the positions of the selected Msubbands, one CQI for the selected M subbands, and a CQI for the totalband or the set S. Herein, the size of a subband and M may vary with thesize of the system band.

1-3) Mode 2-2

The UE simultaneously selects the positions of M preferred subbands anda single precoding matrix for the M preferred subbands on the assumptionthat data is transmitted in the M preferred subbands. Herein, a CQI isdefined per codeword for the M preferred subbands.

The UE additionally generates a wideband CQI for the system band or theset S.

The UE transmits information about the positions of the M preferredsubbands, one CQI for the M selected subbands, a single precoding matrixindex for the M preferred subbands, a wideband precoding matrix index,and a wideband CQI. Herein, the size of a subband and M may vary withthe size of the system band.

1-4) Mode 3-0

The UE generates and reports a wideband CQI.

The UE generates a CQI for each subband on the assumption that data istransmitted in the subband. Herein, even though an RI>1, a CQIrepresents only a CQI value for a first codeword.

1-5) Mode 3-1

The UE generates a single precoding matrix for the system band or theset S.

The UE generates a subband CQI per codeword on the assumption of apreviously generated single precoding matrix for each subband.

The UE generates a wideband CQI on the assumption of a single precodingmatrix. Herein, a CQI for each subband is expressed as a differentialvalue. For example, a subband CQI is defined as a value obtained bysubtracting a wideband CQI index from a subband CQI index (SubbandCQI=subband CQI index−wideband CQI index). Also, the size of a subbandmay vary with the size of the system band.

4. UCI Multiplexing Method of MTC UE

4.1 MTC UE

MTC refers to communication between machines without human intervention.MTC may diversify services and related terminals. At present, an MTCservice field considered most promising is smart metering. A smart meterused for smart metering is at once a measuring device for measuring anamount of using electricity, water, gas, etc. and a transmission devicefor transmitting various related information through a communicationnetwork.

For example, the smart meter transmits an amount of using electricity,water, gas, etc. periodically or aperiodically to a management centerthrough a communication network. The communication network may use alicensed band such as a cellular network or an unlicensed band such as aWi-Fi network. The present invention considers MTC communication over anLTE network which is one of cellular networks.

Regarding an MTC service, a UE should transmit data to an eNBperiodically. Although a data transmission period is different accordingto a setting of a service provider, it is assumed that the datatransmission period is very long. Meanwhile, the basic operation of anMTC UE supporting smart metering is to measure electricity, gas, andwater. Therefore, the smart meter (i.e., the MTC UE) may be installed ina poorer environment than a general terminal. For example, the smartmeter may be installed in a poor communication environment such as abaseband or a shielded place according to a housing type. However, sincesuch an MTC UE does not require a high data rate and has only to satisfya low data rate with long periodicity, additional installation of arelay or an eNB to improve the poor communication environment of the MTCUE may not be cost-effective. Accordingly, it is preferred to supportMTC UEs by utilizing existing networks as much as possible.

The simplest method for overcoming a poor communication environment ofan MTC UE is that the MTC UE repeatedly transmits the same data. Inembodiments of the present invention, since a DL physical channel and/ora UL physical channel is repeatedly transmitted to or received from anMTC UE, stable communication may be provided.

4.2 PUSCH Transmission Power Control

For PUSCH transmission, an MTC UE should receive control information ona PDCCH/E-PDCCH from an eNB. The control information may include aTransmit Power Command (TPC). In embodiments of the present inventiondescribed below, it is defined that ‘A/B’ means A or B.

In regards to a timing for setting PUSCH transmission power in theLTE/LTE-A system, PUSCH transmission power is set according to a TPCwhich has been transmitted on a PDCCH/E-PDCCH, four subframes earlier inFDD, whereas PUSCH transmission power is set according to a DL/ULconfiguration as illustrated in [Table 19] in TDD.

TABLE 19 TDD UL/DL subframe number i Configuration 0 1 2 3 4 5 6 7 8 9 0— — 6 7 4 — — 6 7 4 1 — — 6 4 — — — 6 4 — 2 — — 4 — — — — 4 — — 3 — — 44 4 — — — — — 4 — — 4 4 — — — — — — 5 — — 4 — — — — — — — 6 — — 7 7 5 —— 7 7 —

Referring to [Table 19], for example, in the case of TDD UL/DLconfiguration 0, when the MTC UE transmits a PUSCH in subframe #2, theMTC UE may set PUSCH transmission power according to a TPC included in aPDCCH/E-PDCCH for PUSCH scheduling, transmitted six subframes earlier.

In a wireless access system supporting MTC, a PDCCH/E-PDCCH isrepeatedly transmitted. Accordingly, a timing relationship between a TPCand PUSCH transmission power setting should be established.

In an FDD system, for example, PUSCH transmission power may be setaccording to a TPC included in the last of repeatedly transmittedPDCCHs/E-PDCCHs. TPCs included in the repeatedly transmittedPDCCHs/E-PDCCHs may be the same power control command. Herein, thestarting time of a PUSCH that the MTC UE is to repeatedly transmit maybe set to be apart from the last subframe of a PDCCH/E-PDCCH carryingcontrol information for the PUSCH by a fixed number of subframes (e.g.,K subframes). K may be fixed to be equal to or larger than 4 (K>=4) by asystem setting. The same principle may also be applied to a TDD system.However, a different K value may be set for each subframe according to aTDD UL/DL configuration (refer to [Table 19]).

Preferably, the MTC UE maintains PUSCH transmission power constantduring a repeated PUSCH transmission period. For this purpose, eventhough the MTC UE receives a TPC for PUSCH power adjustment in DCIFormat 3/3A or a PDCCH/E-PDCCH during repeated PUSCH transmissions, theMTC UE may ignore the TPC transmitted in DCI

Format 3/3A or the PDCCH/E-PDCCH. Therefore, the MTC UE does not expecttransmission of DCI Format 3/3A indicating PUSCH power adjustment ortransmission of a PDCCH/E-PDCCH including a TPC during a repeated PUSCHtransmission period.

In another aspect of the present invention, if the MTC UE receives a newDCI Format 3/3A or PDCCH/E-PDCCH including a TPC after repeated PUSCHtransmissions, the MTC UE may set PUSCH power, in further considerationof a TPC received during previous repeated PUSCH transmissions. Forexample, if the MTC UE receives a 1-dB power decrease command in DCIFormat 3/3A during a previous repeated PUSCH transmission period andthen a 1-dB power increase command on a PDCCH/E-PDCCH that schedules aPUSCH, the MTC UE may add −1 dB indicated during the previous repeatedPUSCH transmissions to 1dB indicated for the current repeated PUSCHtransmissions and thus repeatedly transmit the current PUSCH byadjusting the transmission power of the PUSCH by 0 dB.

4.3 PUCCH Transmission Power Control

In MTC, if a PDCCH/E-PDCCH is repeatedly transmitted, a timingrelationship between PUCCH transmission power setting and a TPC shouldbe established. For example, PUCCH transmission power may be setaccording to a TPC included in a PDCCH/E-PDCCH transmitted repeatedly toan MTC UE in an FDD system.

Preferably, the MTC UE maintains PUCCH transmission power constantduring a repeated PUCCH transmission period. For this purpose, if theMTC UE receives a TPC for PUCCH power adjustment in DCI Format 3/3A or aPDCCH/E-PDCCH during repeated PUCCH transmissions, the MTC UE may ignoreDCI Format 3/3A or the PDCCH/E-PDCCH. That is, the MTC UE does notexpect transmission of DCI Format 3/3A or a PDCCH/E-PDCCH indicatingPUCCH power adjustment during a repeated PUCCH transmission period.

However, in another aspect of the present invention, if the MTC UErepeatedly transmits another PUCCH after the repeated PUCCHtransmissions, the MTC UE may set PUCCH transmission power, in furtherconsideration of a TPC included in a newly transmitted DCI format 3/3Aor PDCCH/E-PDCCH. For example, it is assumed that the MTC UE receives a1-dB power decrease command in DCI format 3/3A during a previousrepeated PUCCH transmission period and then a 1-dB power increasecommand on a new PDCCH/E-PDCCH. Herein, the MTC UE may add −1 dBindicated during the previous repeated PUCCH transmissions to 1 dBindicated for the current repeated PUCCH transmissions and thusrepeatedly transmit the current PUCCH by adjusting the transmissionpower of the PUCCH by 0 dB.

4.4 Method for Adjusting UL Transmission Power

A description will be given again of the methods described in sections4.2 and 4.3 with reference to the attached drawings. FIG. 17 is adiagram illustrating a signal flow for a method of adjusting ULtransmission power.

An eNB transmits a first PDCCH or E-PDCCH carrying schedulinginformation for a PUSCH or PUCCH, repeatedly X times. The repeated firstPDCCHs/E-PDCCHs may include first TPCs for adjusting the transmissionpower of the PUSCH or PUCCH (S1710).

An MTC UE may set the transmission power of a first PUSCH/PUCCH based onthe first TPCs included in the first PDCCHs/E-PDCCHs repeatedlytransmitted in step S1710. The first TPCs included in the repeatedlytransmitted first PDCCHs/E-PDCCHs are the same transmit power controlcommand (S1720).

The MTC UE may receive a second PDCCH/E-PDCCH including a new second TPCfor power adjustment from the eNB during the repeated first PUSCH/PUDCCHtransmissions in step S1720 (S1725).

In general, if a PDCCH/E-PDCCH carrying new scheduling information isreceived, a PUSCH/PUCCH is transmitted based on the new schedulinginformation instead of an old scheduling scheme in the LTE/LTE-A system.However, it is preferred that an MTC UE transmits a PUSCH/PUCCH with thesame transmission power during a repeated transmission period.Accordingly, the MTC UE may ignore the second TPC included in the secondPDCCH/E-PDCCH received in step S1725.

Upon receipt of a new third PDCCH/E-PDCCH from the eNB after the MTC UEcompletes step S1720, the MTC UE may transmit a second PUSCH/PUCCHrepeatedly Z times according to scheduling information and a third TPCincluded in the third PDCCH/E-PDCCH (S1740).

In another aspect of the present invention, the MTC UE may adjusttransmission power, taking into account both the second TPC included inthe second PDCCH/E-PDCCH received in step S1720 and the third TPCincluded in the third PDCCH/E-PDCCH received in step S1730. This isbecause the eNB is likely to transmit the second PDCCH/E-PDCCH and/orthe third PDCCH/E-PDCCH so that transmission power may be adjustedaccording to a changed channel situation. Therefore, even though the MTCUE maintains the same transmission power during the repeatedtransmissions in step S1720, the MTC UE may consider both the second andthird TPCs respectively included in the second and third PDCCHs/E-PDCCHsin determining the transmission power of the next PUSCH/PUCCH.

For example, if the second TPC included in the second PDCCH indicates −2dB transmission power adjustment and the third TPC command included inthe third PDCCH indicates +1 dB transmission power adjustment, the MTCUE may transmit the second PUSCH/PUCCH repeatedly Z times with −1 dBtransmission power adjustment in step S1740.

In FIG. 17, the repetition numbers of the first and second PUSCHs/PUCCHsare shown as Y and Z, respectively. However, the transmission numbers ofa PUSCH and a PUCCH may be set to be different.

In embodiments of the present invention, a PDCCH is a physical channeltransmitted in the control channel region of a subframe, and an E-PDCCHis a physical channel transmitted in the data channel region of asubframe. Further, a PUCCH is a physical channel for transmitting UCI,and a PUSCH is a physical channel for transmitting user data.

4.5 Method for Adjusting Transmission Power in Case of Collision betweenPUCCH and PUSCH

In the LTE/LTE-A system, a PDSCH transmission and a PUSCH transmissionare scheduled independently. Therefore, in the case where a PUCCHcarrying UCI (e.g., an HARQ-ACK) and a PUSCH carrying user data arerepeatedly transmitted, a repeated PUCCH transmission period and arepeated PUSCH transmission period may overlap with each other. Ingeneral, the repeated PUCCH transmission period (e.g., N1) is shorterthan the repeated PUSCH transmission period (e.g., N2). That is, it istypical that N1<N2.

It may be regulated that a PUSCH is not transmitted during a repeatedtransmission period of a PUCCH carrying an HARQ-ACK. The number ofsubframes in which PUSCH transmissions are restricted due to PUCCHtransmissions (i.e., the number of subframes in which the PUSCH and thePUCCH are overlapped) may be determined according to N1, N2, thestarting time of the repeated PUCCH transmissions, and the starting timeof the repeated PUSCH transmissions.

Overlaps between repeated PUSCH transmissions and repeated PUCCHtransmissions may be classified into (1) full inclusion of a repeatedPUCCH transmission period in a repeated PUSCH transmission period, and(2) partial inclusion of a repeated PUCCH transmission period in arepeated PUSCH transmission period.

Because the repeated PUCCH transmissions and the repeated PUSCHtransmissions may overlap with each other in time and thus the PUSCH maynot be transmitted in a part or any of subframes, the performance of therepeated PUSCH transmissions may be degraded. Therefore, if the PUSCHtransmissions are restricted due to the PUCCH transmissions, thetransmission power of the PUSCH transmissions may be increased tocompensate for the restriction.

FIG. 18, including views (a) and (b), is a diagram illustrating one ofmethods of adjusting the transmission power of a PUSCH, when repeatedPUCCH transmissions collide with repeated PUSCH transmissions.

In FIG. 18, P1 and P2 represent the transmission power of a PUCCH and aPUSCH, respectively. ΔP represents a power increment for the PUSCH whichhas not been transmitted due to the PUCCH transmission. The value of ΔPmay be set based on the number of subframes in which the PUSCH issupposed to be transmitted but is not transmitted due to repeated PUCCHtransmissions. For example, the value of ΔP may be set in proportion tothe number of PUSCH subframes whose transmission has been discontinued.

In another method, ΔP may be set to a predetermined value irrespectiveof the number of PUSCH subframes not transmitted due to PUCCHtransmissions. For example, the eNB may indicate ΔP to the UE by ahigher-layer signal or on a DL control channel.

In embodiments of the present invention described below, it is assumedthat the repetition number of one of DL control channels, PDCCH/E-PDCCHis N3, and the repetition number of a PDSCH transmitted after Fsubframes as an offset from the repeated PDCCH/E-PDCCH transmissions isN4. To maintain transmission power constant during a repeated PUSCHtransmission period, the MTC UE should start the repeated PUCCHtransmissions and/or the repeated PUSCH transmissions after decodingrepeatedly transmitted PDSCHs, as illustrated in FIG. 18(a). In otherwords, the MTC UE preferably has prior knowledge of the PUCCHtransmissions before the start of the PUSCH transmissions. Accordingly,the MTC UE may preliminarily increase the power of another repeatedPUSCH transmissions by as much as PUSCHs which have not been transmitteddue to the repeated PUCCH transmissions.

FIG. 18(a) illustrates a method of maintaining the transmission power ofa PUSCH constant even when repeated transmissions of a periodic PUCCHare partially overlapped with repeated transmissions of a PUSCH carryinguser data. However, since the repeated PUSCH transmissions arediscontinued in N1 subframes due to the PUCCH, the MTC UE may transmitthe PUSCH repeatedly by increasing the transmission power of the PUSCHby ΔP proportional to N1.

FIG. 18(b) illustrates a method of, when repeated PUSCH transmissionsare discontinued due to repeated PUCCH transmissions, setting differenttransmission power before and after the discontinuation. Consideringthat there is no problem with the PUSCH transmissions before the PUSCHtransmissions are discontinued due to the PUCCH, the MTC UE may transmitthe PUSCH with the original allocated transmission power, P2. When thePUSCH transmissions are discontinued due to the PUCCH transmissions, theMTC UE may transmit the PUSCH with power increased in proportion to thenumber (e.g., N1) of subframes in which the PUSCH transmissions havebeen discontinued due to the PUCCH transmissions.

FIG. 19 is a diagram illustrating one of methods of adjusting thetransmission power of a PUSCH, when repeated PUCCH transmissions collidewith repeated PUSCH transmissions.

In general, a PDSCH transmission and a PUSCH transmission are scheduledindependently. Therefore, if the MTC UE repeatedly transmits a PUCCHcarrying UCI (e.g., an HARQ-ACK) and a PUSCH carrying user data, arepeated PUCCH transmission period may overlap with a repeated PUSCHtransmission period. Herein, it may be configured that the PUCCH istransmitted as many times as its repetition number, with priority overthe PUSCH and thus the PUSCH is not transmitted in the overlappedsubframes.

In this case, the PUSCH may further be transmitted by extending, intime, N1 subframes in which the PUSCH has not been transmitted due tothe repeated PUCCH transmissions, after the repeated PUCCH transmissionsare completed. Thus, the PUSCH may be eventually transmitted as manytimes as a total PUSCH repetition number.

Referring to FIG. 19, when a PUSCH and a PUCCH are overlapped with eachother, the MTC UE completes the whole repeated PUSCH transmissions byperforming repeated PUSCH transmissions which have been discontinued dueto repeated PUCCH transmissions, after completion of the PUCCHtransmissions.

In the foregoing embodiments of the present invention, when repeatedPUCCH transmissions start during a repeated PUSCH transmission period,the eNB needs to determine whether a PUCCH has been transmitted, due tothe error probability of a PDCCH transmitted to the UE. However, if therepeated PUCCH transmission period is overlapped only with the last somesubframes of the repeated PUSCH transmission period, it may be difficultto determine whether the PUCCH has been transmitted.

Therefore, if the PUCCH transmission period does not overlap with thePUSCH transmission period by a predetermined part or more (e.g., ½ ormore of the repeated PUCCH transmission period), The MTC UE may assumeno PUCCH transmission. In other words, in the case where repeated PUSCHtransmissions overlap with repeated PUCCH transmissions, the MTC UEassumes that only when a predetermined part or more of the repeatedPUCCH transmission period (½ or more of the repeated PUCCH transmissionperiod) overlaps with the repeated PUSCH transmission period, therepeated PUCCH transmissions start.

5. Apparatuses

Apparatuses illustrated in FIG. 20 are means that can implement themethods described before with reference to FIGS. 1 to 19.

A UE may act as a transmission end on a UL and as a reception end on aDL. An eNB may act as a reception end on a UL and as a transmission endon a DL.

That is, each of the UE and the eNB may include a Transmitter (Tx) 2040or 2050 and a Receiver (Rx) 2060 or 2070, for controlling transmissionand reception of information, data, and/or messages, and an antenna 2000or 2010 for transmitting and receiving information, data, and/ormessages.

Each of the UE and the eNB may further include a processor 2020 or 2030for implementing the afore-described embodiments of the presentdisclosure and a memory 2080 or 2090 for temporarily or permanentlystoring operations of the processor 2020 or 2030.

The embodiments of the present invention may be implemented using theabove-described components and functions of a UE and an eNB. Forexample, the processor of the MTC UE and/or the processor of the eNB maysupport implementation of the methods of repeatedly transmitting a PUCCHand a PUSCH, described before in section 4. Preferably, the PUCCH/PUSCHis transmitted repeatedly with the same transmission power. Accordingly,if the MTC UE receives a PDCCH/E-PDCCH including a TPC for transmissionpower adjustment during repeated PUCCH/PUSCH transmissions, the MTC UEmay ignore the PDCCH/E-PDCCH. However, upon receipt of a newPDCCH/E-PDCCH after completion of the repeated PUCCH/PUSCHtransmissions, the MTC UE may transmit a PUCCH/PUSCH with transmissionpower adjusted based on a TPC included in the PDCCH/E-PDCCH. Fordetails, refer to section 4 and FIG. 17.

In the case where a PUCCH and a PUSCH overlap with each other in one ormore subframes, the PUCCH may be transmitted with priority over thePUSCH and thus the

PUSCH may not be transmitted. In this case, the PUSCH may be transmittedwith transmission power increased in proportion to the number ofoverlapped subframes. For details, refer to section 4 and FIGS. 18 and19.

The Tx and Rx of the UE and the eNB may perform a packetmodulation/demodulation function for data transmission, a high-speedpacket channel coding function, OFDMA packet scheduling, TDD packetscheduling, and/or channelization. Each of the UE and the eNB of FIG. 20may further include a low-power Radio Frequency (RF)/IntermediateFrequency (IF) module.

Meanwhile, the UE may be any of a Personal Digital Assistant (PDA), acellular phone, a Personal Communication Service (PCS) phone, a GlobalSystem for Mobile (GSM) phone, a Wideband Code Division Multiple Access(WCDMA) phone, a Mobile Broadband System (MBS) phone, a hand-held PC, alaptop PC, a smart phone, a Multi Mode-Multi Band (MM-MB) terminal, etc.

The smart phone is a terminal taking the advantages of both a mobilephone and a PDA. It incorporates the functions of a PDA, that is,scheduling and data communications such as fax transmission andreception and Internet connection into a mobile phone. The MB-MMterminal refers to a terminal which has a multi-modem chip built thereinand which can operate in any of a mobile Internet system and othermobile communication systems (e.g. CDMA 2000, WCDMA, etc.).

Embodiments of the present disclosure may be achieved by various means,for example, hardware, firmware, software, or a combination thereof

In a hardware configuration, the methods according to exemplaryembodiments of the present disclosure may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, the methods according to theembodiments of the present disclosure may be implemented in the form ofa module, a procedure, a function, etc. performing the above-describedfunctions or operations. A software code may be stored in the memory2080 or 2090 and executed by the processor 2020 or 2030. The memory islocated at the interior or exterior of the processor and may transmitand receive data to and from the processor via various known means.

Those skilled in the art will appreciate that the present disclosure maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent disclosure. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment of the presentdisclosure or included as a new claim by a subsequent amendment afterthe application is filed.

The present disclosure is applicable to various wireless access systemsincluding a 3GPP system, a 3GPP2 system, and/or an IEEE 802.xx system.Besides these wireless access systems, the embodiments of the presentdisclosure are applicable to all technical fields in which the wirelessaccess systems find their applications.

What is claimed is:
 1. A method for controlling uplink transmissionpower in a wireless access system, the method performed by a UserEquipment (UE) and comprising: receiving control information for aPhysical Uplink Shared Channel (PUSCH); and repeatedly transmitting aPUSCH as a predetermined number of times based on the controlinformation, wherein the PUSCH is repeatedly transmitted with atransmission power which is maintained constant during a time period forthe repeated PUSCH transmissions.
 2. The method according to claim 1,wherein the repeatedly transmitted PUSCHs have same uplink data.
 3. Themethod according to claim 1, wherein the control information istransmitted through a Physical Downlink Control Channel (PDCCH) and thePDCCH is repeatedly transmitted.
 4. The method according to claim 3,wherein a starting time of the PUSCH is set to be separated from a timepoint of the repeatedly transmitted PDCCH by K subframes, and wherein Kis equal to or greater than 4 for Frequency Division Duplexing (FDD), orK is set for each subframe according to a Downlink (DL)/Uplink (UL)configuration for a Time Division Duplexing (TDD).
 5. The methodaccording to claim 1, wherein the transmission power is set according tothe control information which has been transmitted K subframes before.6. The method according to claim 3, wherein the repeatedly transmittedPDCCHs have same control information.
 7. The method according to claim1, wherein the wireless access system supports a Machine TypeCommunication (MTC), and the UE is an MTC UE supporting the MTC.